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/domain/__init__.py

@@ -0,0 +1,28 @@
+"""Domain layer for the auth plugin."""
+
+from app.plugins.auth.domain.config import AuthConfig, load_auth_config_from_env
+from app.plugins.auth.domain.errors import AuthErrorCode, AuthErrorResponse, TokenError, token_error_to_code
+from app.plugins.auth.domain.jwt import TokenPayload, create_access_token, decode_token
+from app.plugins.auth.domain.models import User, UserResponse
+from app.plugins.auth.domain.password import hash_password, hash_password_async, verify_password, verify_password_async
+from app.plugins.auth.domain.service import AuthService, AuthServiceError
+
+__all__ = [
+    "AuthConfig",
+    "AuthErrorCode",
+    "AuthErrorResponse",
+    "AuthService",
+    "AuthServiceError",
+    "TokenError",
+    "TokenPayload",
+    "User",
+    "UserResponse",
+    "create_access_token",
+    "decode_token",
+    "hash_password",
+    "hash_password_async",
+    "load_auth_config_from_env",
+    "token_error_to_code",
+    "verify_password",
+    "verify_password_async",
+]