fix: run cities labeler from its release image

Pull git.cosocial.info/cosocial-canada/atproto-cosocial-labeler instead of
cloning and building on the server, which took several minutes per deploy.
Watchtower picks up new :latest releases.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

vars/main.yml.example

@@ -59,8 +59,7 @@ pds_operator_hostname: pds-operator.cosocial.ca
 
 # Cities labeler (DM-driven city badges, serves labels at pds_cities_hostname)
 # pds_cities_enabled: true
-# pds_cities_repo: https://git.cosocial.info/CoSocial-Canada/atproto-cosocial-labeler.git
-# pds_cities_version: main
+# pds_cities_image: git.cosocial.info/cosocial-canada/atproto-cosocial-labeler:latest
 # pds_cities_hostname: cities-labeler.cosocial.ca
 # pds_cities_handle: cities.pds.cosocial.ca
 # pds_cities_app_password: CHANGE_ME   # app password with DM access