Add project CLAUDE.md and ignore machine-local .claude files

- CLAUDE.md: project guidance for Claude Code (repo layout, commands,
  architecture, no-collapse guardrails).
- .gitignore: exclude .claude/settings.local.json and .claude/*.local.*
  (personal permission allowlists and transient ralph-loop session state).

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

.gitignore

@@ -174,3 +174,7 @@ cython_debug/
 # PyPI configuration file
 .pypirc
 
+# Claude Code (machine-local, not shared)
+.claude/settings.local.json
+.claude/*.local.*
+