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-SETUP.md

@@ -369,19 +369,19 @@ The `instance_data` volume persists:
 
 ```
 flask-shopdb/
-├── docker-compose.yml          # Main stack definition
-├── docker-compose.backup.yml   # Backup service
-├── Dockerfile                  # Multi-stage build
-├── .env                        # Environment config (gitignored)
-├── corp-root-ca.pem            # Zscaler cert (gitignored)
-├── certs/                      # TLS certificates (gitignored)
-│   ├── server.crt
-│   └── server.key
-├── scripts/
-│   ├── docker-entrypoint.sh    # Container startup
-│   └── bootstrap-plugins.sh    # Plugin auto-install
-└── deploy/
-    └── site-profile-universal.json  # Full plugin list
+|-- docker-compose.yml          # Main stack definition
+|-- docker-compose.backup.yml   # Backup service
+|-- Dockerfile                  # Multi-stage build
+|-- .env                        # Environment config (gitignored)
+|-- corp-root-ca.pem            # Zscaler cert (gitignored)
+|-- certs/                      # TLS certificates (gitignored)
+|   |-- server.crt
+|   +-- server.key
+|-- scripts/
+|   |-- docker-entrypoint.sh    # Container startup
+|   +-- bootstrap-plugins.sh    # Plugin auto-install
++-- deploy/
+    +-- site-profile-universal.json  # Full plugin list
 ```
 
 ## Next Steps