Refactor geo cache persistence into repository + remove raw SQL from tasks/main, update task list

backend/app/main.py

@@ -161,11 +161,7 @@ async def _lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
     await geo_service.load_cache_from_db(db)
 
     # Log unresolved geo entries so the operator can see the scope of the issue.
-    async with db.execute(
-        "SELECT COUNT(*) FROM geo_cache WHERE country_code IS NULL"
-    ) as cur:
-        row = await cur.fetchone()
-        unresolved_count: int = int(row[0]) if row else 0
+    unresolved_count = await geo_service.count_unresolved(db)
     if unresolved_count > 0:
         log.warning("geo_cache_unresolved_ips", unresolved=unresolved_count)