Add Jenkins CI and Portainer stack for image deployment

Jenkinsfile builds and pushes both the firebase (nginx/static) and
sqlite (caddy+node) images to thinkserver:5000, guarded to main only.
docker/portainer-stack.yml deploys the prebuilt sqlite image from the
registry behind the external TLS-terminating nginx.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker/portainer-stack.yml

@@ -0,0 +1,27 @@
+# docker/portainer-stack.yml — Portainer stack for the SQLite/server build.
+# Deploys the prebuilt image from the local registry (built + pushed by Jenkins).
+# Paste into Portainer's web editor (Stacks -> Add stack -> Web editor).
+#
+# TLS is terminated by the external nginx, which should reverse_proxy to
+# http://<docker-host>:8080  (and pass the WebSocket upgrade headers for /ws).
+services:
+  app:
+    image: thinkserver:5000/ttrpg-tracker-sqlite:latest
+    container_name: ttrpg-tracker
+    ports:
+      - "8080:80"                     # host:container — nginx upstream is :8080
+    volumes:
+      - app-data:/data                # SQLite DB lives here; back this up
+    environment:
+      - DB_PATH=/data/tracker.sqlite
+      - PORT=4001                     # node backend port (internal; caddy proxies to it)
+    restart: unless-stopped
+    healthcheck:
+      test: ["CMD", "wget", "-qO-", "http://localhost:80/"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 10s
+
+volumes:
+  app-data: