docs: add multi-machine setup guide

Add comprehensive guide for using this config across multiple machines
(personal, work, etc.) without branch conflicts.

Changes:
- Add MULTI-MACHINE-SETUP.md with complete setup instructions
- Add CLAUDE-LOCAL.md.example as template for machine-specific overrides
- Update .gitignore to exclude CLAUDE-LOCAL.md and *-local.json patterns
- Update README.md to reference multi-machine setup guide

Key features:
- Layered configuration approach (shared + local overrides)
- No branch conflicts - local overrides are git-ignored
- Same repo works with different Claude Code credentials
- Supports work/personal machines with different standards

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitignore

@@ -18,9 +18,15 @@ secrets/
 *.secret
 
 # =============================================================================
-# MACHINE-SPECIFIC STATE
+# MACHINE-SPECIFIC STATE AND OVERRIDES
 # =============================================================================
 
+# Machine-specific overrides (work preferences, personal additions)
+CLAUDE-LOCAL.md
+*-local.json
+*-LOCAL.md
+local/
+
 # Conversation history (contains project-specific and personal conversations)
 history.jsonl
 history.*.jsonl