feat(ops): add usage_logs partitioning check at deployment startup

Add CheckUsageLogsPartitioning function that:
- Checks if usage_logs table is partitioned
- Warns with prominent banner if not partitioned and rows > 100K
- Provides actionable guidance for manual partition migration

This helps operators identify performance risks early and take
appropriate action before data volume causes issues.

backend/internal/setup/setup.go

@@ -362,7 +362,13 @@ func initializeDatabase(cfg *SetupConfig) error {
 
 	migrationCtx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
 	defer cancel()
-	return repository.ApplyMigrations(migrationCtx, db)
+	if err := repository.ApplyMigrations(migrationCtx, db); err != nil {
+		return err
+	}
+
+	// 检查 usage_logs 分区状态（仅在首次部署时提示）
+	repository.CheckUsageLogsPartitioning(migrationCtx, db)
+	return nil
 }
 
 func createAdminUser(cfg *SetupConfig) (bool, string, error) {