Migrate CI from Jenkins to Gitea Actions

Replaces the Jenkinsfile with a .gitea/workflows/build-push.yml that
builds on pushes to main and pushes `latest` + `sha-<short>` tags to the
Gitea package registry using the REGISTRY_URL variable and
REGISTRY_TOKEN secret. Adds a docker-compose.yml that pulls the
published image for deployment.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-push.yml

@@ -0,0 +1,38 @@
+name: Build and Push Image
+
+on:
+  push:
+    branches: [main]
+
+env:
+  IMAGE: josh/workweekprogress
+
+jobs:
+  build-push:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Compute short SHA
+        id: vars
+        run: echo "sha_short=${GITHUB_SHA::7}" >> "$GITHUB_OUTPUT"
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to Gitea registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ vars.REGISTRY_URL }}
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.REGISTRY_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: |
+            ${{ vars.REGISTRY_URL }}/${{ env.IMAGE }}:latest
+            ${{ vars.REGISTRY_URL }}/${{ env.IMAGE }}:sha-${{ steps.vars.outputs.sha_short }}