QUA-1806: Restructure Unique check docs into multi-page section

[RafaelOsiro]

Overview

Restructures the Unique check from a single page into a multi-page section (data-quality-checks/unique/) with Introduction, How It Works, Examples, API, and FAQ. Each Examples scenario now ships with its own Mermaid flowchart and equivalent SQL block. Corrects several factual gaps surfaced during a code-verified review pass (notably the is_element_context property for Array fields, and the fact that anomaly_message_field does not apply to Unique because the check emits only Shape Anomalies). Tightens copy across the sub-tree, removes em-dashes, and standardizes Accepted Types and Anomaly Types tables sitewide on MDI icons. Also fixes the API Permissions table on the Self-Hosted License Permissions page.

The How to Create page is authored but temporarily commented out from the nav and from the Introduction card grid until step screenshots are added in a follow-up.

Key Changes

Unique sub-tree (new section under data-quality-checks/unique/):

• New pages: introduction.md, how-it-works.md, examples.md, api.md, faq.md. Old unique-check.md deleted; mkdocs.yml nav and redirect_maps updated so legacy URLs point to the new Introduction.
• examples.md: three tabbed scenarios (Single-Field Primary Key, Composite Key on Order Items, Scoped Uniqueness with Filter), each with its own scenario-specific Mermaid flowchart and equivalent SQL block. Custom Anomaly Description removed from Scenario 3 (it has no effect on Shape-only checks). "What gets flagged" phrasing standardized across all three scenarios.
• how-it-works.md: long-form semantics covering evaluation flow, single vs. composite, NULL handling, filter behavior, coverage, anomaly message format, and relationship with other rule types. Polished across multiple review rounds: single-field example in the 4-step flow, partial-NULL phrasing, optimized path wording, concrete coverage warning, K-count explanation in plain English, factual correction of the "Not Null" pairing row.
• introduction.md: tightened H1 to "Unique Check", renamed "In-Depth Overview" to "Overview", removed the NULL admonition (now lives in How It Works), condensed Typical use cases, reworded Field Scope, and updated the Next Steps card grid (How to Create card commented out pending screenshots).
• api.md: corrected properties description to mention is_element_context for Array fields; coverage default made explicit (1, strict mode); added the "Not applicable to Unique" caveat to anomaly_message_field; intro paragraph smoothed; removed single-item tab wrapper.
• faq.md: Q7 properties answer corrected for the Array case; added missing How It Works link in Related; new Q on Custom Anomaly Description not applying to Unique; standardized on line_number placeholder; Unicode ellipsis replaced with ASCII dots.
• how-to-create.md: authored content with a TODO HTML comment noting the page is hidden until screenshots are restored from a local stash.
• All em-dashes dropped from the sub-tree.

Sitewide check-page alignment:

• components/anomaly-support/index.md: standardized on MDI icons (:material-check-circle: green for supported, :material-close-circle: red for not-supported); removed text-negative and grayscale color classes from Type labels.
• 39 other check pages in data-quality-checks/: replaced :octicons-check-16: with the green MDI check and added the missing "Supported" header to the Accepted Types tables.

Other:

• self-hosted/license/deep-dive/permissions.md: replaced the Markdown API Permissions table with an HTML equivalent and explicit colgroup widths so /license/expiration no longer wraps mid-word.
• overview-of-a-check.md and rule-types-overview.md: links updated to the new Unique Introduction.

Pages to Test

• http://localhost:8000/data-quality-checks/unique/introduction/ - H1 reads "Unique Check", section is "Overview", no NULL admonition, Accepted Types and Anomaly Types tables both show MDI icons with "Supported" headers.
• http://localhost:8000/data-quality-checks/unique/how-it-works/ - no em-dashes, "Field order doesn't affect duplicate detection" admonition, NULL section intact, K-count explanation reads cleanly, Not Null pairing row says "a second NULL row becomes a duplicate of the first".
• http://localhost:8000/data-quality-checks/unique/examples/ - three tabs, each with its own flowchart and equivalent SQL block. Scenario 3 shows Custom Anomaly Description: Off and "anomaly_message_field": null.
• http://localhost:8000/data-quality-checks/unique/api/ - Field Notes table: properties mentions is_element_context for Array fields, coverage defaults to 1, anomaly_message_field has the "Not applicable to Unique" caveat. Payload renders as a plain code fence (no tab chrome).
• http://localhost:8000/data-quality-checks/unique/faq/ - four questions in Configuration section (including Custom Anomaly Description), Related section has four links including How It Works.
• http://localhost:8000/data-quality-checks/unique-check/ - should redirect to the new Introduction.
• http://localhost:8000/data-quality-checks/overview-of-a-check/ - Unique row links to the new Introduction.
• http://localhost:8000/data-quality-checks/rule-types-overview/ - Unique row links to the new Introduction.
• Spot-check 3 other check pages of different shapes for Accepted Types alignment (e.g., not-null-check.md, contains-email-check.md, min-value-check.md).
• http://localhost:8000/self-hosted/license/deep-dive/permissions/#api-permissions - verify /license/expiration no longer wraps mid-word.

[greptile-apps]

Greptile Summary

This PR restructures the Unique check documentation from a single flat page into a five-page section (introduction, how-it-works, examples, api, faq), adds per-example Mermaid flowcharts, and performs a sitewide standardization of Accepted-Types and Anomaly-Types table icons from Octicons to MDI icons across 39 existing check pages.

• New unique/ section: Five new pages replace the deleted unique-check.md; MkDocs nav and two redirect-map entries are updated so legacy URLs route to the new Introduction without breaking existing links.
• Sitewide icon alignment: anomaly-support/index.md now emits green :material-check-circle: and red :material-close-circle: icons instead of the old Octicons check and empty cells; all 39 affected check pages receive the same replacement for their Accepted Types tables, and the second-column header is standardized to "Supported".
• permissions.md fix: Markdown API Permissions table replaced with explicit HTML + colgroup widths to prevent /license/expiration from wrapping.

Confidence Score: 5/5

Documentation-only change with no runtime code; safe to merge.

All changes are Markdown, HTML table markup, and MkDocs configuration. The deleted page is covered by two redirect-map entries, the navigation is consistent with the new structure, cross-page links use correct relative paths from the new unique/ subdirectory, and the sitewide icon replacement is driven by a single shared include-markdown component so all 39 affected pages stay in sync. No executable code was modified.

No files require special attention.

Important Files Changed

Filename	Overview
docs/data-quality-checks/unique/introduction.md	New Introduction hub page with definition, two-mode overview, Accepted Types table (MDI icons), and Next Steps card grid; How to Create card correctly commented out pending screenshots.
docs/data-quality-checks/unique/how-it-works.md	Detailed semantics page covering evaluation flow, single vs. composite key, NULL handling, filter clause, coverage, anomaly format, relationship table, and performance notes; no issues found.
docs/data-quality-checks/unique/examples.md	Three tabbed scenarios (single-field, composite key, scoped with filter), each with payload, sample data, anomaly message, flowchart, and equivalent SQL; SQL and anomaly counts are internally consistent.
docs/data-quality-checks/unique/api.md	API reference page with full payload example and field-notes table; correctly documents that anomaly_message_field is silently ignored for shape-only rules.
docs/data-quality-checks/unique/faq.md	FAQ covering composite-key semantics, NULL handling, filter ordering, violation counts, shape-only anomaly type, and configuration variants; answers are consistent with how-it-works.md.
docs/components/anomaly-support/index.md	Replaced Octicons check icons and empty-cell unsupported markers with MDI green check-circle / red close-circle icons; removes text-negative/grayscale CSS classes from type label divs. Sitewide include-markdown pull means all 39 check pages render the updated icons automatically.
mkdocs.yml	Nav entry for Unique expanded to a five-page sub-section (How to Create commented out); two redirect_maps entries added so legacy /unique-check/ URLs forward to the new Introduction.
docs/self-hosted/license/deep-dive/permissions.md	Markdown API Permissions table replaced with HTML table plus explicit colgroup widths; fixes word-wrap on /license/expiration endpoint cell.
docs/data-quality-checks/unique-check.md	Old single-page Unique check file deleted; URL is covered by a redirect_maps entry in mkdocs.yml pointing to the new Introduction.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    OLD["unique-check.md\n(single page, deleted)"]
    REDIRECT["redirect_maps in mkdocs.yml\n/unique-check/ to /unique/introduction/"]

    subgraph NEW["New unique/ section"]
        INTRO["introduction.md\nDefinition · Field Scope\nAccepted Types · Anomaly Types\nNext Steps card grid"]
        HIW["how-it-works.md\nEvaluation flow · NULL handling\nFilter · Coverage · Anomaly format\nRelated rule types"]
        HTC["how-to-create.md\nCommented out of nav\npending screenshots"]
        EX["examples.md\nSingle-Field PK\nComposite Key\nScoped with Filter"]
        API["api.md\nPayload example\nField notes table"]
        FAQ["faq.md\nBehavior · Anomaly Reporting\nConfiguration"]
    end

    OLD -->|deleted + redirect| REDIRECT
    REDIRECT --> INTRO
    INTRO --> HIW
    INTRO -.->|hidden| HTC
    INTRO --> EX
    INTRO --> API
    INTRO --> FAQ

    subgraph SITEWIDE["Sitewide icon change (39 check pages)"]
        ANOM["anomaly-support/index.md\nOcticons to MDI icons\nempty cell to red close-circle"]
    end

    ANOM -->|include-markdown| INTRO

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