fix(missing-skus): reconcile stale false positives against Oracle

SKUs mapped externally (via SSH script or direct SQL) never triggered
resolve_missing_sku(), leaving them stuck as unresolved=0 indefinitely.
New reconcile_unresolved_missing_skus() revalidates ALL unresolved SKUs
against Oracle at sync, rescan, and CSV import time. Fail-soft on Oracle
down. Clears the 7 prod false positives on next sync or manual rescan.

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

api/app/routers/mappings.py

@@ -8,7 +8,7 @@ from typing import Optional
 import io
 import asyncio
 
-from ..services import mapping_service, sqlite_service
+from ..services import mapping_service, sqlite_service, validation_service
 
 import logging
 logger = logging.getLogger(__name__)
@@ -168,6 +168,7 @@ async def import_csv(file: UploadFile = File(...)):
     content = await file.read()
     text = content.decode("utf-8-sig")
     result = mapping_service.import_csv(text)
+    await validation_service.reconcile_unresolved_missing_skus()
     return result
 
 @router.get("/api/mappings/export-csv")