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/plugins/auth/api/__init__.py

@@ -0,0 +1,17 @@
+"""HTTP API layer for the auth plugin."""
+
+from app.plugins.auth.api.router import (
+    ChangePasswordRequest,
+    LoginResponse,
+    MessageResponse,
+    RegisterRequest,
+    router,
+)
+
+__all__ = [
+    "ChangePasswordRequest",
+    "LoginResponse",
+    "MessageResponse",
+    "RegisterRequest",
+    "router",
+]