fix: don't commit agent worktrees

`git add -A` swept .claude/worktrees/ into the previous commit as embedded git
repositories. They are transient checkouts created for parallel agent runs and
have no business in the tree — removed from the index and gitignored.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitignore

@@ -47,3 +47,6 @@ test-mcp.sh
 
 # Claude Code local state
 .claude/scheduled_tasks.lock
+
+# Agent worktrees — transient checkouts, never part of the repo
+.claude/worktrees/