feat: support private repo cloning with HTTP basic auth

- Add SSH URL detection with friendly prompt to use HTTPS instead
- Add private repo toggle (default off) with username/password fields
- Persist auth_type and credential in repositories table
- Pass stored credentials to PullRepo for authenticated pulls
- Incremental migration adds auth_type and credential columns

handlers/repos.go

@@ -149,8 +149,9 @@ func (h *ReposHandler) PullRepo(c *gin.Context) {
 	}
 
 	id := c.Param("id")
-	var localPath string
-	err := h.db.QueryRow(`SELECT local_path FROM repositories WHERE id = ? AND user_id = ?`, id, user.ID).Scan(&localPath)
+	var localPath, authType string
+	var credential sql.NullString
+	err := h.db.QueryRow(`SELECT local_path, auth_type, credential FROM repositories WHERE id = ? AND user_id = ?`, id, user.ID).Scan(&localPath, &authType, &credential)
 	if err == sql.ErrNoRows {
 		c.JSON(http.StatusNotFound, gin.H{"error": "repository not found"})
 		return
@@ -160,7 +161,19 @@ func (h *ReposHandler) PullRepo(c *gin.Context) {
 		return
 	}
 
-	result, err := services.PullRepo(localPath)
+	// Parse stored credentials
+	var username, password string
+	if authType == "basic" && credential.Valid {
+		var cred struct {
+			Username string `json:"username"`
+			Password string `json:"password"`
+		}
+		json.Unmarshal([]byte(credential.String), &cred)
+		username = cred.Username
+		password = cred.Password
+	}
+
+	result, err := services.PullRepo(localPath, username, password)
 	if err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 		return
@@ -238,10 +251,23 @@ func (h *ReposHandler) CloneRepo(c *gin.Context) {
 		return
 	}
 
+	// Determine auth type and credential for persistence
+	authType := "none"
+	var credential *string
+	if req.Username != "" || req.Password != "" {
+		authType = "basic"
+		credJSON, _ := json.Marshal(map[string]string{
+			"username": req.Username,
+			"password": req.Password,
+		})
+		s := string(credJSON)
+		credential = &s
+	}
+
 	// Save to database with user_id
 	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)
+	res, err := h.db.Exec(`INSERT INTO repositories (user_id, url, local_path, size_bytes, cloned_at, last_used, auth_type, credential) VALUES (?, ?, ?, ?, ?, ?, ?, ?)`,
+		user.ID, req.URL, repoDir, result.SizeBytes, now, now, authType, credential)
 	if err != nil {
 		sendEvent("error", map[string]interface{}{"message": "save to db: " + err.Error()})
 		return