chore(deploy): hardened prod compose, rollout script, and CI for the server

docker-compose.prod.yml targets the server: Postgres is never published, the
app binds to 127.0.0.1 (Caddy proxies it), and every service has a memory/CPU cap
plus no-new-privileges / cap_drop / read-only rootfs. deploy/deploy.sh rolls out
main with a host-side build (migrations run via the entrypoint). CI type-checks
and builds the frontend and byte-compiles the backend on every push to main.

.forgejo/workflows/ci.yml

@@ -0,0 +1,35 @@
+name: CI
+# Lightweight validation on every push to main: type-check + build the frontend and
+# byte-compile the backend. The image build and rollout happen on the the VPS host
+# (see deploy/README.md); this just catches breakage early.
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  frontend:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+      - run: npm ci
+        working-directory: frontend
+      - run: npx tsc --noEmit
+        working-directory: frontend
+      - run: npm run build
+        working-directory: frontend
+
+  backend:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - run: pip install -r requirements.txt
+        working-directory: backend
+      - run: python -m compileall -q app
+        working-directory: backend