fix: replace unicode characters and fix finalize-restore endpoint

Style check fixes:
- Replace unicode box-drawing characters with ASCII (|-- instead of ├──)
- Replace emoji status markers with [OK]/[FAIL]/[WARN] tags
- Replace arrows (→ with ->, ↔ with <->) and em-dashes (— with --)
- Add venv-quick to excluded directories in check script
- Exclude darkwing report files (findings.sarif, report.md)

Backup finalization fix:
- Fix finalize-restore endpoint to not claim the upgrade sentinel
- Endpoint now checks for pending upgrade and returns {queued: true}
- Leaves UPGRADE_SENTINEL for background watcher to claim and process
- Prevents inline Alembic runs that can outlast request timeout

Claude Code context:
- Add .claude/ directory with INDEX.md and QUICK-REFERENCE.md
- Add CLAUDE.md with project overview and conventions
- Helps Claude Code understand project structure and rules

Fixes failing test: test_the_endpoint_does_not_run_the_upgrade_itself
Fixes naming/style CI check violations

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

DOCKER-PREBUILT-APPROACH.md

@@ -83,9 +83,9 @@ https://localhost:5001
 
 | Approach | Build Time | Corporate Proxy | Complexity | Production Ready |
 |----------|-----------|----------------|------------|------------------|
-| Multi-stage Dockerfile | 15+ min | ❌ Fails | High | ❌ No |
-| Pre-built frontend | 2-3 min | ✅ Works | Medium | ⚠️ Yes (with CI/CD) |
-| Pre-built images from registry | 30 sec | ✅ Works | Low | ✅ Yes |
+| Multi-stage Dockerfile | 15+ min | [FAIL] Fails | High | [FAIL] No |
+| Pre-built frontend | 2-3 min | [OK] Works | Medium | [WARN] Yes (with CI/CD) |
+| Pre-built images from registry | 30 sec | [OK] Works | Low | [OK] Yes |
 
 ## Next Steps