chore: update Docker and CI for web + backend architecture

Replace scraper container with backend API container. Web image no
longer mounts a data volume or ships SQLite. Backend image runs Hono
server with node-cron scheduler, owns the database exclusively.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitea/workflows/deploy.yml

@@ -27,10 +27,10 @@ jobs:
           push: true
           tags: ${{ vars.REGISTRY }}/${{ gitea.repository_owner }}/sixflagssupercalendar:web
 
-      - name: Build and push scraper image
+      - name: Build and push backend image
         uses: docker/build-push-action@v6
         with:
           context: .
-          target: scraper
+          target: backend
           push: true
-          tags: ${{ vars.REGISTRY }}/${{ gitea.repository_owner }}/sixflagssupercalendar:scraper
+          tags: ${{ vars.REGISTRY }}/${{ gitea.repository_owner }}/sixflagssupercalendar:backend