chore: ignore per-session worktrees

A worktree under .claude/ is a full copy of the repo, dist/ included.
Left untracked it gets picked up as source — in ai-forms an identical
setup made the lint gate report 10 errors that were all in a stale
worktree, and blocked a release for reasons that had nothing to do with
the code being released.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: Mao Nakamoto

.gitignore

@@ -1,3 +1,6 @@
 node_modules/
 dist/
 *.tgz
+# Per-session git worktrees. Never lint, test, or publish from these — a stale
+# copy of the repo here is otherwise picked up as if it were source.
+.claude/