fix(auth): revert to Better-Auth session-cookie auth, preserve email-in feature

- Revert auth/dependencies.py, auth/routes.py, services/auth.py, schemas.py
  to Better-Auth session-cookie auth (removed JWT register/login/refresh)
- Preserve GET /auth/me/email-in-address endpoint
- Fix UUIDString TypeDecorator: process_result_value returns uuid.UUID
  (not str) so SQLAlchemy 2.0 sentinel tracking matches UUID-to-UUID
- Fix seed_data fixture: look up real user_id from session token via
  sessions table; purchases now reference actual user FK
- Update purchase_data fixture to use session-cookie auth
- Update test_auth_endpoints, test_auth_validation to cookie-based tests
- Remove TestRegistrationErrors and TestLoginErrors (no longer applicable)
- Update test_openapi.py expected routes and count
- Update test_error_handler.py to use PATCH /auth/me validation

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/cartsnitch_api/schemas.py

@@ -6,28 +6,8 @@ from uuid import UUID
 from pydantic import BaseModel, EmailStr, Field
 
 # ---------- Auth ----------
-
-
-class RegisterRequest(BaseModel):
-    email: EmailStr
-    password: str = Field(min_length=8, max_length=128)
-    display_name: str = Field(min_length=1, max_length=100)
-
-
-class LoginRequest(BaseModel):
-    email: EmailStr
-    password: str
-
-
-class RefreshRequest(BaseModel):
-    refresh_token: str
-
-
-class TokenResponse(BaseModel):
-    access_token: str
-    refresh_token: str
-    token_type: str = "bearer"
-    expires_in: int
+# Registration, login, and session management are handled by Better-Auth (auth/ service).
+# These schemas are for the profile management endpoints only.
 
 
 class UpdateUserRequest(BaseModel):
@@ -285,6 +265,13 @@ class ErrorResponse(BaseModel):
     code: str | None = None
 
 
+# ---------- Email-In ----------
+
+class EmailInAddressResponse(BaseModel):
+    email_address: str
+    instructions: str
+
+
 # Rebuild forward refs
 ProductDetailResponse.model_rebuild()
 PriceTrendResponse.model_rebuild()