Fix last_repo persistence: fallback to user_repos table and add debug logging

Backend:
- Add GetMostRecentUserRepo query to get most recent repo from user_repos
- Update GetCurrentUser to check user_repos if users.last_repo is empty
- Add debug logging to track last_repo flow

Frontend:
- Add debug logging to Dashboard useEffect to track repo detection

This ensures users are redirected to their previously selected repo after login,
even if users.last_repo is empty but user_repos has entries.

backend/internal/api/handlers/auth.go

···
 		return
 	}
 
+	log.Printf("[DEBUG] GetCurrentUser: userID=%d, last_repo from users table='%s'", userID, user.LastRepo)
+
+	lastRepo := user.LastRepo
+
+	// If last_repo is empty, try to get the most recent repo from user_repos table
+	if lastRepo == "" {
+		log.Printf("[DEBUG] last_repo empty, checking user_repos table")
+		mostRecentRepo, err := h.db.GetMostRecentUserRepo(userID)
+		if err != nil {
+			log.Printf("[DEBUG] Error getting most recent repo: %v", err)
+		} else if mostRecentRepo != nil {
+			lastRepo = mostRecentRepo.RepoName
+			log.Printf("[DEBUG] Found repo in user_repos table: %s", lastRepo)
+
+			// Also update the users table for next time
+			if err := h.db.UpdateUserRepo(userID, lastRepo); err != nil {
+				log.Printf("[DEBUG] Failed to update users.last_repo: %v", err)
+			}
+		} else {
+			log.Printf("[DEBUG] No repos found in user_repos table")
+		}
+	}
+
 	response := UserResponse{
 		ID:        user.ID,
 		Username:  user.Username,
 		AvatarURL: user.AvatarURL,
 		Provider:  "github",
-		LastRepo:  user.LastRepo,
+		LastRepo:  lastRepo,
 	}
+
+	log.Printf("[DEBUG] GetCurrentUser response: ID=%d, LastRepo='%s'", response.ID, response.LastRepo)
 
 	w.Header().Set("Content-Type", "application/json")
 	json.NewEncoder(w).Encode(response)

backend/internal/database/queries.go

···
 	return repos, nil
 }
 
+// GetMostRecentUserRepo gets the most recently used repo from user_repos table
+func (db *DB) GetMostRecentUserRepo(userID int) (*UserRepo, error) {
+	query := `
+		SELECT id, user_id, repo_name, repo_link, last_used_at, created_at, updated_at
+		FROM user_repos
+		WHERE user_id = ?
+		ORDER BY last_used_at DESC
+		LIMIT 1
+	`
+
+	var repo UserRepo
+	err := db.QueryRow(query, userID).Scan(
+		&repo.ID, &repo.UserID, &repo.RepoName, &repo.RepoLink,
+		&repo.LastUsedAt, &repo.CreatedAt, &repo.UpdatedAt,
+	)
+
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("failed to get most recent user repo: %w", err)
+	}
+
+	return &repo, nil
+}
+
 func (db *DB) DeleteBranchState(userID int, repoFullName string) error {
 	query := `
 		DELETE FROM branch_states

frontend/src/components/dashboard/DashboardApp.tsx

···
 
   // Check for last_repo or URL params and redirect if needed
   useEffect(() => {
-    if (userLoading || !user) return;
+    console.log('[DEBUG] Dashboard useEffect running, userLoading:', userLoading, 'user:', user);
+    
+    if (userLoading || !user) {
+      console.log('[DEBUG] Still loading user or no user, returning early');
+      return;
+    }
 
     // Check URL params first
     const urlParams = new URLSearchParams(window.location.search);
     const repoParam = urlParams.get('repo');
+    console.log('[DEBUG] URL repo param:', repoParam);
 
     if (repoParam) {
       // Parse repo from URL (format: owner/repo)
       const [owner, repo] = repoParam.split('/');
       if (owner && repo) {
+        console.log('[DEBUG] Setting repo from URL param:', owner, repo);
         setRepoConfig({ owner, repo, folder: '' });
         return;
       }
     }
 
     // Check user's last_repo
+    console.log('[DEBUG] Checking user.last_repo:', user.last_repo);
     if (user.last_repo) {
       const [owner, repo] = user.last_repo.split('/');
       if (owner && repo) {
+        console.log('[DEBUG] Setting repo from user.last_repo:', owner, repo);
         setRepoConfig({ owner, repo, folder: '' });
         return;
       }
     }
 
     // No repo configured, redirect to select-repo page
+    console.log('[DEBUG] No repo found, redirecting to /select-repo');
     window.location.href = '/select-repo';
   }, [user, userLoading]);