chore: gitignore local agent/planning notes

Adds .gitignore entries for .claude/, CLAUDE.md, and docs/superpowers/
so local IDE/agent planning artifacts don't get committed by accident.

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

Author: d-v-b

.gitignore

@@ -91,3 +91,8 @@ tests/.hypothesis
 
 zarr/version.py
 zarr.egg-info/
+
+# Local agent / planning notes (not versioned)
+.claude/
+CLAUDE.md
+docs/superpowers/