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>

LOCAL-DEV-SETUP.md

@@ -322,27 +322,27 @@ Flask's `flask run` command uses an auto-reloader that spawns a subprocess. This
 
 ```
 flask-shopdb/
-├── .env                    # Local environment config (gitignored)
-├── run_dev.py              # Local development launcher
-├── shopdb/                 # Flask application
-│   ├── __init__.py         # App factory
-│   ├── config.py           # Configuration classes
-│   ├── core/               # Core models and APIs
-│   └── plugins/            # Plugin manager
-├── plugins/                # Plugin packages
-│   ├── backups/
-│   ├── computers/
-│   └── ...
-├── frontend/               # Vue 3 SPA
-│   ├── src/
-│   └── dist/               # Production build (gitignored)
-├── instance/               # Runtime state (gitignored)
-│   ├── plugins.json        # Plugin registry
-│   └── ...
-├── migrations/             # Core Alembic migrations
-├── scripts/                # Deployment and backup scripts
-├── backups/                # Local backup storage (gitignored)
-└── tests/                  # Test suite
+|-- .env                    # Local environment config (gitignored)
+|-- run_dev.py              # Local development launcher
+|-- shopdb/                 # Flask application
+|   |-- __init__.py         # App factory
+|   |-- config.py           # Configuration classes
+|   |-- core/               # Core models and APIs
+|   +-- plugins/            # Plugin manager
+|-- plugins/                # Plugin packages
+|   |-- backups/
+|   |-- computers/
+|   +-- ...
+|-- frontend/               # Vue 3 SPA
+|   |-- src/
+|   +-- dist/               # Production build (gitignored)
+|-- instance/               # Runtime state (gitignored)
+|   |-- plugins.json        # Plugin registry
+|   +-- ...
+|-- migrations/             # Core Alembic migrations
+|-- scripts/                # Deployment and backup scripts
+|-- backups/                # Local backup storage (gitignored)
++-- tests/                  # Test suite
 ```
 
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