Relates to CODAGT-432
Adds three new search filters to the chat list endpoint (`GET
/api/experimental/chats/`):
- `pr:<number>` - exact PR number match
- `repo:<owner/repo>` - substring match against git remote origin or URL
- `pr_title:<text>` - case-insensitive PR title substring match
Includes SQL filter clauses (EXISTS against `chat_diff_statuses`),
parser with validation, handler wiring, unit tests, swagger annotation
update, and a new search syntax documentation page.
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Cian Johnston
15ada66e14