ci: push to GHCR from the Gitea workflow instead of a separate one

The Gitea instance's act_runner is the CI that actually executes here;
GitHub Actions on the mirror isn't confirmed to run at all (and a
push-mirror lacking the "workflow" PAT scope can silently drop
.github/workflows changes anyway). Add a GHCR login/push to the
existing .gitea/workflows/docker-publish.yml job instead, so one
build produces tags on both the Gitea registry and ghcr.io. Drop the
now-redundant .github/workflows/docker-publish.yml.

Requires a new repo secret GHCR_TOKEN: a GitHub PAT with write:packages
scope (separate from REGISTRY_TOKEN, which is scoped to the Gitea
registry).

.gitea/workflows/docker-publish.yml

@@ -27,6 +27,13 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.REGISTRY_TOKEN }}
 
+      - name: Log in to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GHCR_TOKEN }}
+
       - name: Build and push
         uses: docker/build-push-action@v6
         with:
@@ -35,3 +42,5 @@ jobs:
           tags: |
             ${{ vars.REGISTRY_HOST }}/${{ env.IMAGE_NAME }}:latest
             ${{ vars.REGISTRY_HOST }}/${{ env.IMAGE_NAME }}:${{ github.sha }}
+            ghcr.io/${{ env.IMAGE_NAME }}:latest
+            ghcr.io/${{ env.IMAGE_NAME }}:${{ github.sha }}

.github/workflows/docker-publish.yml

@@ -1,37 +0,0 @@
-name: Publish Docker image
-
-on:
-  push:
-    branches: [main, master]
-    tags: ['v*']
-
-permissions:
-  contents: read
-  packages: write
-
-jobs:
-  build-and-push:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-
-      - uses: docker/setup-buildx-action@v3
-
-      - name: Compute lowercase image name
-        run: echo "IMAGE_NAME=$(echo '${{ github.repository }}' | tr '[:upper:]' '[:lower:]')" >> "$GITHUB_ENV"
-
-      - name: Log in to GHCR
-        uses: docker/login-action@v3
-        with:
-          registry: ghcr.io
-          username: ${{ github.actor }}
-          password: ${{ secrets.GITHUB_TOKEN }}
-
-      - name: Build and push
-        uses: docker/build-push-action@v6
-        with:
-          context: .
-          push: true
-          tags: |
-            ghcr.io/${{ env.IMAGE_NAME }}:latest
-            ghcr.io/${{ env.IMAGE_NAME }}:${{ github.sha }}