gitea: use git.k8s.syd1.au.unkin.net ROOT_URL for testing

Points the new gitea at its k8s route so it can be exercised before the git.unkin.net data cutover (whose ROOT_URL flip is the final migration step).

- set DOMAIN/ROOT_URL/SSH_DOMAIN to git.k8s.syd1.au.unkin.net

Claude-Session: https://claude.ai/code/session_015ur3i7D2azsMAWTSVABApv

apps/overlays/au-syd1/gitea/values.yaml

@@ -125,9 +125,9 @@ gitea:
 
   config:
     server:
-      DOMAIN: git.unkin.net
-      ROOT_URL: https://git.unkin.net/
-      SSH_DOMAIN: git.unkin.net
+      DOMAIN: git.k8s.syd1.au.unkin.net
+      ROOT_URL: https://git.k8s.syd1.au.unkin.net/
+      SSH_DOMAIN: git.k8s.syd1.au.unkin.net
       DISABLE_SSH: true
       START_SSH_SERVER: false
       LFS_START_SERVER: true