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>

docker-compose.yml

@@ -0,0 +1,7 @@
+services:
+  dayDrain:
+    image: gitea.thewrightserver.net/josh/workweekprogress:latest
+    container_name: day-drain
+    restart: unless-stopped
+    ports:
+      - "5000:5000"