fix: Prevent GitHub API rate limiting from frequent worktree PR fetching

Fixes #685

This commit addresses the GitHub API rate limit issue caused by excessive worktree PR status fetching.

## Changes

### Server-side PR caching (list.ts)
- Added `GitHubPRCacheEntry` interface and `githubPRCache` Map
- Implemented 2-minute TTL cache for GitHub PR data
- Modified `fetchGitHubPRs()` to check cache before making API calls
- Added `forceRefresh` parameter to bypass cache when explicitly requested
- Cache is properly cleared when force refresh is triggered

### Frontend polling reduction (worktree-panel.tsx)
- Increased worktree polling interval from 5 seconds to 30 seconds
- Reduces polling frequency by 6x while keeping UI reasonably fresh
- Updated comment to reflect new polling strategy

### Type improvements (use-worktrees.ts)
- Fixed `fetchWorktrees` callback signature to accept `silent` option
- Returns proper type for removed worktrees detection

## Impact
- Combined ~12x reduction in GitHub API calls
- 2-minute cache prevents repeated API hits during normal operation
- 30-second polling balances responsiveness with API conservation
- Force refresh option allows users to manually update when needed

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/server/src/routes/worktree/routes/list.ts

@@ -39,8 +39,15 @@ interface GitHubRemoteCacheEntry {
   checkedAt: number;
 }
 
+interface GitHubPRCacheEntry {
+  prs: Map<string, WorktreePRInfo>;
+  fetchedAt: number;
+}
+
 const githubRemoteCache = new Map<string, GitHubRemoteCacheEntry>();
+const githubPRCache = new Map<string, GitHubPRCacheEntry>();
 const GITHUB_REMOTE_CACHE_TTL_MS = 5 * 60 * 1000; // 5 minutes
+const GITHUB_PR_CACHE_TTL_MS = 2 * 60 * 1000; // 2 minutes - avoid hitting GitHub on every poll
 
 interface WorktreeInfo {
   path: string;
@@ -180,9 +187,24 @@ async function getGitHubRemoteStatus(projectPath: string): Promise<GitHubRemoteS
  * This also allows detecting PRs that were created outside the app.
  *
  * Uses cached GitHub remote status to avoid repeated warnings when the
- * project doesn't have a GitHub remote configured.
+ * project doesn't have a GitHub remote configured. Results are cached
+ * briefly to avoid hammering GitHub on frequent worktree polls.
  */
-async function fetchGitHubPRs(projectPath: string): Promise<Map<string, WorktreePRInfo>> {
+async function fetchGitHubPRs(
+  projectPath: string,
+  forceRefresh = false
+): Promise<Map<string, WorktreePRInfo>> {
+  const now = Date.now();
+
+  if (!forceRefresh) {
+    const cached = githubPRCache.get(projectPath);
+    if (cached && now - cached.fetchedAt < GITHUB_PR_CACHE_TTL_MS) {
+      return cached.prs;
+    }
+  } else {
+    githubPRCache.delete(projectPath);
+  }
+
   const prMap = new Map<string, WorktreePRInfo>();
 
   try {
@@ -225,6 +247,11 @@ async function fetchGitHubPRs(projectPath: string): Promise<Map<string, Worktree
         createdAt: pr.createdAt,
       });
     }
+
+    githubPRCache.set(projectPath, {
+      prs: prMap,
+      fetchedAt: Date.now(),
+    });
   } catch (error) {
     // Silently fail - PR detection is optional
     logger.warn(`Failed to fetch GitHub PRs: ${getErrorMessage(error)}`);
@@ -364,7 +391,7 @@ export function createListHandler() {
       // Only fetch GitHub PRs if includeDetails is requested (performance optimization).
       // Uses --state all to detect merged/closed PRs, limited to 1000 recent PRs.
       const githubPRs = includeDetails
-        ? await fetchGitHubPRs(projectPath)
+        ? await fetchGitHubPRs(projectPath, forceRefreshGitHub)
         : new Map<string, WorktreePRInfo>();
 
       for (const worktree of worktrees) {