Stop tracking CLAUDE.md and add it to .gitignore

CLAUDE.md holds local project guidance for Claude Code and should not be
version-controlled. Remove it from the index with `git rm --cached` (the
working-tree copy is preserved) and add it to .gitignore so future edits
stay local.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: AlpineArchitecture

.gitignore

@@ -24,6 +24,7 @@ backend/static/
 # Dev / scratch
 _archive/
 .claude/
+CLAUDE.md
 generate_ai.py
 PROMPT.personal.md
 screenshot_*.png