docs: specs, requirements, ux-flows and traceability for new features

Add specs for the account menu, downloads-as-offline-library, offline
downloaded-only filter, and scoped search (+ boundary revision). Add the
new UR/DR entries to requirements.md, update ux-flows, and regenerate the
traceability matrix.

TRACES: UR-049, UR-050, UR-052, UR-053, UR-054, UR-055, UR-056

docs/traceability-ci.md

@@ -12,22 +12,22 @@ The CI/CD pipeline automatically validates that code changes are properly traced
 
 ## Gitea Actions Workflows
 
-Two workflows are configured in `.gitea/workflows/`:
+Traceability validation lives in `.gitea/workflows/traceability-check.yml`:
 
-### 1. `traceability-check.yml` (Primary - Recommended)
-Gitea-native workflow with:
 - ✅ Automatic trace extraction
 - ✅ Coverage validation against minimum threshold (50%)
 - ✅ Modified file checking
 - ✅ Artifact preservation
 - ✅ Summary reports
 
-**Runs on:** Every push and pull request
+**Runs on:** Every push and pull request to `master`/`main`/`develop`
 
-### 2. `traceability.yml` (Alternative)
-GitHub-compatible workflow with additional features:
-- Pull request comments with coverage stats
-- GitHub-specific integrations
+A second workflow, `traceability.yml`, previously duplicated this one as a
+"GitHub-compatible alternative". It was removed: CI here is Gitea Actions, and
+its only unique step (PR comments via `actions/github-script`) depended on the
+GitHub REST client, which Gitea does not provide. To add PR comments, post to
+Gitea's `/api/v1/repos/{owner}/{repo}/issues/{index}/comments` from
+`traceability-check.yml` rather than reviving the old file.
 
 ## What Gets Validated