chore: add .gitignore (session state and local files stay out of git)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HBbjgS5A55RVavoyjJC4FX

.gitignore

@@ -0,0 +1,36 @@
+# Local configuration
+*.local.md
+*.local.json
+*.local.sh
+
+# MCP configuration (may contain API keys)
+.mcp.json
+
+# Secrets
+.env
+*.key
+*.pem
+credentials.*
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Editor files
+*.swp
+*.swo
+*~
+
+# Temporary files
+*.tmp
+*.bak
+
+# npm
+node_modules/
+
+# session/local state (gitignored per polyrepo convention)
+STATE.md
+REMEMBER.md
+/ROADMAP.md
+TODO.md
+.claude/