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/app/routers/articles.py

@@ -0,0 +1,10 @@
+from fastapi import APIRouter, Query
+
+from ..services import article_service
+
+router = APIRouter(prefix="/api/articles", tags=["articles"])
+
+@router.get("/search")
+def search_articles(q: str = Query("", min_length=2)):
+    results = article_service.search_articles(q)
+    return {"results": results}