refactor: enforce strict architecture rules and add Pydantic response models

- Update architecture rules to be stricter (API-003 now blocks ALL exception
  raising in endpoints, not just HTTPException)
- Update get_current_vendor_api dependency to guarantee token_vendor_id presence
- Remove redundant _get_vendor_from_token helpers from all vendor API files
- Move vendor access validation to service layer methods
- Add Pydantic response models for media, notification, and payment endpoints
- Add get_active_vendor_by_code service method for public vendor lookup
- Add get_import_job_for_vendor service method with vendor validation
- Update validation script to detect exception raising patterns in endpoints

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/api/v1/vendor/team.py

@@ -164,7 +164,7 @@ def invite_team_member(
     )
 
 
-@router.post("/accept-invitation", response_model=InvitationAcceptResponse)
+@router.post("/accept-invitation", response_model=InvitationAcceptResponse)  # public
 def accept_invitation(acceptance: InvitationAccept, db: Session = Depends(get_db)):
     """
     Accept a team invitation and activate account.