feat(app): add plugin system with auth plugin and static assets

Add new application structure:
- app/main.py - application entry point
- app/plugins/ - plugin system with auth plugin:
  - api/ - REST API endpoints and schemas
  - authorization/ - auth policies, providers, hooks
  - domain/ - business logic (service, models, jwt, password)
  - injection/ - route injection and guards
  - ops/ - operational utilities
  - runtime/ - runtime configuration
  - security/ - middleware, CSRF, dependencies
  - storage/ - user repositories and models
- app/static/ - static assets (scalar.js for API docs)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/main.py

@@ -0,0 +1,15 @@
+"""Entry point for running the Gateway API via `python app/main.py`.
+
+Useful for IDE debugging (e.g., PyCharm / VS Code debug configurations).
+Equivalent to: PYTHONPATH=. uvicorn app.gateway.app:app --host 0.0.0.0 --port 8001
+"""
+
+import uvicorn
+
+if __name__ == "__main__":
+    uvicorn.run(
+        "app.gateway.app:app",
+        host="0.0.0.0",
+        port=8001,
+        reload=True,
+    )