chore: add .claude/ to gitignore and untrack it

The .claude/ directory holds local Claude Code settings that should
not be version-controlled. Add it to .gitignore and remove the
already-committed settings from the index (files kept on disk).

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

.gitignore

@@ -7,6 +7,7 @@ config.json
 cookies/
 .superpowers/
 .worktrees/
+.claude/
 setup.log
 /bin/
 scripts/navbar_bigger.png