feat: add FastAPI admin dashboard with sync orchestration and test suite

Replace Flask admin with FastAPI app (api/app/) featuring:
- Dashboard with stat cards, sync control, and history
- Mappings CRUD for ARTICOLE_TERTI with CSV import/export
- Article autocomplete from NOM_ARTICOLE
- SKU pre-validation before import
- Sync orchestration: read JSONs -> validate -> import -> log to SQLite
- APScheduler for periodic sync from UI
- File logging to logs/sync_comenzi_YYYYMMDD_HHMMSS.log
- Oracle pool None guard (503 vs 500 on unavailable)

Test suite:
- test_app_basic.py: 30 tests (imports + routes) without Oracle
- test_integration.py: 9 integration tests with Oracle

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

api/requirements.txt

@@ -1,5 +1,10 @@
-Flask==2.3.2
-Flask-CORS==4.0.0
-oracledb==1.4.2
-python-dotenv==1.0.0
-gunicorn==21.2.0
+fastapi==0.115.6
+uvicorn[standard]==0.34.0
+jinja2==3.1.4
+python-multipart==0.0.18
+oracledb==2.5.1
+aiosqlite==0.20.0
+apscheduler==3.10.4
+python-dotenv==1.0.1
+pydantic-settings==2.7.1
+httpx==0.28.1