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/storage/models.py

@@ -0,0 +1,25 @@
+from __future__ import annotations
+
+from sqlalchemy import Boolean, Integer, String, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column
+
+from store.persistence.base_model import Base
+
+
+class User(Base):
+    """Application user table."""
+
+    __tablename__ = "users"
+    __table_args__ = (
+        UniqueConstraint("oauth_provider", "oauth_id", name="uq_users_oauth_identity"),
+        {"comment": "Application user table."},
+    )
+
+    id: Mapped[str] = mapped_column(String(64), primary_key=True, unique=True, index=True)
+    email: Mapped[str] = mapped_column(String(255), unique=True, index=True)
+    password_hash: Mapped[str | None] = mapped_column(String(255), default=None)
+    system_role: Mapped[str] = mapped_column(String(16), default="user", index=True)
+    oauth_provider: Mapped[str | None] = mapped_column(String(64), default=None)
+    oauth_id: Mapped[str | None] = mapped_column(String(255), default=None)
+    needs_setup: Mapped[bool] = mapped_column(Boolean, default=False)
+    token_version: Mapped[int] = mapped_column(Integer, default=0)