feat(handoff): preview report template without projects

[Kairo-J]

Show a clearly labeled, data-free template when no active Project is configured. Render preview values as em dashes and allow retrying the Project catalog without creating placeholder data.

Guard against stale catalog responses, add template contract coverage, and update the localized server UI documentation.

Refs #1256

Which issue or RFC does this PR close?

Closes #1256.

Rationale for this change

When the active Project catalog is empty, the Handoff Report page currently collapses into a generic empty state. That leaves users without a clear view of the report structure or the information a configured Project will provide.

A clearly labeled, data-free preview makes the expected report shape visible without creating a Project, fabricating report data, or implying that any work has been observed.

What changes are included in this PR?

• Show a dedicated Handoff Report template preview when the active Project catalog is empty.
• Mark the page as a preview and render every report value as an em dash (—) instead of a real status or count.
• Keep only Retry available so users can reload the Project catalog after configuring a Project elsewhere.
• Replace the preview automatically with the canonical report when an active Project becomes available.
• Preserve the current Project search, Workstream navigation, unified Handoff editor, continuity timeline, and Activity UI for real reports.
• Gate catalog assignment behind the current request check so a stale authentication request cannot overwrite newer page state.
• Add a focused server-rendered template contract test and update the English and Chinese Server UI documentation.

This change does not modify public APIs, persisted formats, or Project creation behavior.

Are there any user-facing changes?

Yes. Users with no active Project now see a complete, explicitly labeled report template instead of a generic empty state. The preview contains neutral em dashes only and does not expose Project search, period filters, Markdown download, or Handoff editing actions that cannot work without a Project.

English

中文

How was this change tested?

• make check
• make test — 627 passed, 13 skipped
• make docs-test
• Focused Dashboard and locale tests — 8 passed
• Manual Chrome validation in English and Chinese with an empty Project catalog
• Verified both optional-auth startup and token-authenticated startup
• Verified Retry reloads an empty catalog and switches to the real searchable/editor report after a Project is created
• Verified the preview exposes only Retry, all preview values are em dashes, and the browser console has no errors

AI usage statement

OpenAI Codex (GPT-5) was used to analyze issue #1256, implement and integrate the UI behavior with the latest master, refine tests and documentation, and validate the result in Chrome.