chore: gitignore .claude/ harness scratch dir

Ignores the Claude Code harness's scheduled-task lock and session state
so they don't end up tracked by accident.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bokelley

.gitignore

@@ -160,3 +160,6 @@ IMPLEMENTATION_PLAN.md
 IMPLEMENTATION_SUMMARY.md
 TESTING_STATUS.md
 IMPLEMENTATION_PLAN.md
+
+# Claude Code harness scratch — scheduled-task lock, session state, etc.
+.claude/