docs: clarify API product model descriptions

[Lucas-FManager]

Fixes #1699

Summary

• Removed the unresolved TODO from APISearchRequest.filter.
• Replaced vague filter descriptions with concise metadata-filter guidance and examples.
• Clarified search_memory_type and plugin source descriptions without changing fields, defaults, or validation.

Root Cause

The generated API documentation was exposing placeholder/vague schema descriptions, including an unresolved TODO and ambiguous filter examples.

Validation

• python -m py_compile src/memos/api/product_models.py
• git diff --check
• rg 'TODO: maybe add detailed description later|router diff search|and or or|Filter for the memory' src/memos/api/product_models.py -> no matches

Security

Documentation/schema metadata only. No auth, permission checks, persistence, retrieval logic, network behavior, or secret handling changed.

[Memtensor-AI]

LGTM

Clean documentation-only change. The descriptions are clearer, the TODO is resolved, and the filter examples now use valid syntax instead of the ambiguous "`and` or `or`" key. No logic, defaults, or validation affected.

One minor suggestion:

• The multi-line description strings inside triple-quoted Field(...) blocks (lines ~114, ~407, ~833) will include leading whitespace in the generated OpenAPI schema. Consider using textwrap.dedent or parenthesized string concatenation (as you already do for search_memory_type and source) for consistent rendering in Swagger/Redoc. Not a blocker — just a cosmetic inconsistency across the same file.

Ship it.

[Lucas-FManager]

Thanks for the review. I pushed 93938ea2 to address the whitespace note by replacing the three indented triple-quoted Field(...) descriptions with parenthesized string literals.

Validation:

• python -m py_compile src/memos/api/product_models.py
• git diff --check

Security/behavior note: this remains documentation/schema metadata only; no request validation, defaults, auth, persistence, networking, or secret-handling behavior changed.