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/runtime/__init__.py

@@ -0,0 +1,5 @@
+"""Runtime state utilities for the auth plugin."""
+
+from app.plugins.auth.runtime.config_state import get_auth_config, reset_auth_config, set_auth_config
+
+__all__ = ["get_auth_config", "reset_auth_config", "set_auth_config"]

backend/app/plugins/auth/runtime/config_state.py

@@ -0,0 +1,27 @@
+"""Runtime state holder for auth configuration."""
+
+from __future__ import annotations
+
+from app.plugins.auth.domain.config import AuthConfig, load_auth_config_from_env
+
+_auth_config: AuthConfig | None = None
+
+
+def get_auth_config() -> AuthConfig:
+    global _auth_config
+    if _auth_config is None:
+        _auth_config = load_auth_config_from_env()
+    return _auth_config
+
+
+def set_auth_config(config: AuthConfig) -> None:
+    global _auth_config
+    _auth_config = config
+
+
+def reset_auth_config() -> None:
+    global _auth_config
+    _auth_config = None
+
+
+__all__ = ["get_auth_config", "reset_auth_config", "set_auth_config"]