fix: stop repeated GitHub PR fetch warnings for non-GitHub repos

When opening a git repository without a GitHub remote, the server logs
were spammed with warnings every 5 seconds during worktree polling:

  WARN [Worktree] Failed to fetch GitHub PRs: Command failed: gh pr list
  ... no git remotes found

This happened because fetchGitHubPRs() ran `gh pr list` without first
checking if the project has a GitHub remote configured.

Changes:
- Add per-project cache for GitHub remote status with 5-minute TTL
- Check cache before attempting to fetch PRs, skip silently if no remote
- Add forceRefreshGitHub parameter to clear cache on manual refresh
- Pass forceRefreshGitHub when user clicks the refresh worktrees button

This allows users to add a GitHub remote and immediately detect it by
clicking the refresh button, while preventing log spam during normal
polling for projects without GitHub remotes.

apps/ui/src/components/views/board-view/worktree-panel/hooks/use-worktrees.ts

@@ -39,7 +39,10 @@ export function useWorktrees({
           logger.warn('Worktree API not available');
           return;
         }
-        const result = await api.worktree.listAll(projectPath, true);
+        // Pass forceRefreshGitHub when this is a manual refresh (not silent polling)
+        // This clears the GitHub remote cache so users can re-detect after adding a remote
+        const forceRefreshGitHub = !silent;
+        const result = await api.worktree.listAll(projectPath, true, forceRefreshGitHub);
         if (result.success && result.worktrees) {
           setWorktrees(result.worktrees);
           setWorktreesInStore(projectPath, result.worktrees);

apps/ui/src/lib/electron.ts

@@ -1596,10 +1596,15 @@ function createMockWorktreeAPI(): WorktreeAPI {
       return { success: true, worktrees: [] };
     },
 
-    listAll: async (projectPath: string, includeDetails?: boolean) => {
+    listAll: async (
+      projectPath: string,
+      includeDetails?: boolean,
+      forceRefreshGitHub?: boolean
+    ) => {
       console.log('[Mock] Listing all worktrees:', {
         projectPath,
         includeDetails,
+        forceRefreshGitHub,
       });
       return {
         success: true,

apps/ui/src/lib/http-api-client.ts

@@ -1724,8 +1724,8 @@ export class HttpApiClient implements ElectronAPI {
     getStatus: (projectPath: string, featureId: string) =>
       this.post('/api/worktree/status', { projectPath, featureId }),
     list: (projectPath: string) => this.post('/api/worktree/list', { projectPath }),
-    listAll: (projectPath: string, includeDetails?: boolean) =>
-      this.post('/api/worktree/list', { projectPath, includeDetails }),
+    listAll: (projectPath: string, includeDetails?: boolean, forceRefreshGitHub?: boolean) =>
+      this.post('/api/worktree/list', { projectPath, includeDetails, forceRefreshGitHub }),
     create: (projectPath: string, branchName: string, baseBranch?: string) =>
       this.post('/api/worktree/create', {
         projectPath,

apps/ui/src/types/electron.d.ts

@@ -705,7 +705,8 @@ export interface WorktreeAPI {
   // List all worktrees with details (for worktree selector)
   listAll: (
     projectPath: string,
-    includeDetails?: boolean
+    includeDetails?: boolean,
+    forceRefreshGitHub?: boolean
   ) => Promise<{
     success: boolean;
     worktrees?: Array<{