feat: add SessionRating model and analytics schemas

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -17,6 +17,7 @@ from .refresh_token import RefreshToken
 from .audit_log import AuditLog
 from .password_reset_token import PasswordResetToken
 from .session_share import SessionShare, SessionShareView
+from .session_rating import SessionRating
 from .account_limit_override import AccountLimitOverride
 from .feature_flag import FeatureFlag, PlanFeatureDefault, AccountFeatureOverride
 from .platform_setting import PlatformSetting
@@ -47,6 +48,7 @@ __all__ = [
     "PasswordResetToken",
     "SessionShare",
     "SessionShareView",
+    "SessionRating",
     "AccountLimitOverride",
     "FeatureFlag",
     "PlanFeatureDefault",