Migrate CI to Gitea Actions

Adds .gitea/workflows/docker-build-push.yml (build+push to
gitea.blairhaus.net/pmb/finger-web, matching yttrx-welcomebot's pattern
for the same admin.yttrx.com deploy target) now that GitHub is retired.

.gitea/workflows/docker-build-push.yml

@@ -0,0 +1,33 @@
+name: docker-build-push
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  build-push:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      # act_runner bind-mounts the admin host's real Docker socket into every
+      # job container (Docker-outside-of-Docker, not a nested daemon), so
+      # `docker` here talks straight to the host's daemon — no separate
+      # dockerd to start. Deploy to admin.yttrx.com stays manual (docker
+      # compose pull && up -d there), matching yttrx-welcomebot's pattern for
+      # the same host.
+      - name: Build and push image
+        env:
+          REGISTRY_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+        run: |
+          SHA="${{ github.sha }}"
+          IMAGE="gitea.blairhaus.net/pmb/finger-web"
+
+          docker build -t "$IMAGE:$SHA" -t "$IMAGE:latest" .
+          printf '%s' "$REGISTRY_TOKEN" | docker login gitea.blairhaus.net -u pmb --password-stdin
+          docker push "$IMAGE:$SHA"
+          docker push "$IMAGE:latest"
+          docker logout gitea.blairhaus.net
+
+          echo "pushed $IMAGE:$SHA and $IMAGE:latest"