fix(git): guard getWorktreeStatus against deleted worktree path

When the coordinator closes, its worktree directory is deleted before
the frontend stops polling get_worktree_status. exec('git', ..., { cwd })
throws ENOENT (misleadingly reported as 'spawn git ENOENT') when the cwd
no longer exists. Return a safe empty result instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: brooksc

electron/ipc/git.ts

@@ -1352,6 +1352,9 @@ export async function getWorktreeStatus(
   has_uncommitted_changes: boolean;
   current_branch: string | null;
 }> {
+  if (!fs.existsSync(worktreePath)) {
+    return { has_committed_changes: false, has_uncommitted_changes: false, current_branch: null };
+  }
   const { stdout: statusOut } = await exec('git', ['status', '--porcelain'], {
     cwd: worktreePath,
     maxBuffer: MAX_BUFFER,