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/authorization/registry.py

@@ -0,0 +1,23 @@
+"""Registry/build helpers for default authorization evaluators."""
+
+from __future__ import annotations
+
+from collections.abc import Callable
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from app.plugins.auth.authorization.authorization import PolicyEvaluator
+
+
+PolicyChainBuilder = Callable[[], tuple["PolicyEvaluator", ...]]
+
+
+def build_default_policy_evaluators() -> tuple["PolicyEvaluator", ...]:
+    """Return the default policy chain for auth-plugin authorization."""
+
+    from app.plugins.auth.authorization.authorization import evaluate_owner_policy
+
+    return (evaluate_owner_policy,)
+
+
+__all__ = ["PolicyChainBuilder", "build_default_policy_evaluators"]