feat(schemas): T17 add Pydantic auth schemas

Add authentication schemas for user registration and login:
- UserRegister: email, password (with strength validation), password_confirm
- UserLogin: email, password
- UserResponse: id, email, created_at, is_active (orm_mode=True)
- TokenResponse: access_token, token_type, expires_in
- TokenData: user_id, exp

Includes field validators for password strength and password confirmation matching.

Test coverage: 19 tests for all schemas

src/openrouter_monitor/schemas/__init__.py

@@ -0,0 +1,16 @@
+"""Schemas package for OpenRouter Monitor."""
+from openrouter_monitor.schemas.auth import (
+    TokenData,
+    TokenResponse,
+    UserLogin,
+    UserRegister,
+    UserResponse,
+)
+
+__all__ = [
+    "UserRegister",
+    "UserLogin",
+    "UserResponse",
+    "TokenResponse",
+    "TokenData",
+]