docs: add agent guidelines, architecture specs, and decision records

- Add AGENTS.md defining coding standards, security, and workflows

- Add GEMINI.md and CLAUDE.md referencing AGENTS.md

- Add docs/ARCHITECTURE.md detailing MCP server design and OpenProject API integration

- Add docs/DECISIONS.md with initial ADRs (stack, transport, auth, scoping)

- Add .gitignore for Node.js and secrets protection

.gitignore

@@ -0,0 +1,30 @@
+# Dependencies
+node_modules/
+.pnpm-store/
+
+# Build artifacts
+dist/
+build/
+coverage/
+
+# Environment variables & secrets
+.env
+.env.*
+!.env.example
+
+# IDE & Editor files
+.idea/
+.vscode/
+*.swp
+*.swo
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*