fix: use MySQL-compatible datetime format for cloned_at

RFC3339 format (T separator, Z suffix) is rejected by MySQL DATETIME columns.
Use '2006-01-02 15:04:05' instead.

handlers/repos.go

@@ -239,7 +239,7 @@ func (h *ReposHandler) CloneRepo(c *gin.Context) {
 	}
 
 	// Save to database with user_id
-	now := time.Now().Format(time.RFC3339)
+	now := time.Now().Format("2006-01-02 15:04:05")
 	res, err := h.db.Exec(`INSERT INTO repositories (user_id, url, local_path, size_bytes, cloned_at, last_used) VALUES (?, ?, ?, ?, ?, ?)`,
 		user.ID, req.URL, repoDir, result.SizeBytes, now, now)
 	if err != nil {