docs(deploy): correct the image size, and say what a missing rgcom runner does

The image measures 757 MB, not the ~600 MB the requirements table guessed. And
until the rgcom runner exists the deploy job simply queues, which is worth stating
in both the workflow and DEPLOY.md: build has already published the image by then,
so the manual pull works throughout and the queued job goes when the runner does.

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

.gitea/workflows/build-image.yml

@@ -114,6 +114,10 @@ jobs:
     runs-on: rgcom
     # Guard against a workflow_dispatch fired from a branch: only main is deployed.
     if: github.ref == 'refs/heads/main'
+    # Until a runner with this label exists, this job simply QUEUES. That is the
+    # intended behaviour and it breaks nothing: `build` has already published the
+    # image, so `docker compose pull && up -d` by hand is available the whole time,
+    # and the queued job runs the moment the runner registers.
 
     steps:
       - name: Pull the fresh image and recreate the container