Add Gitea Actions workflow to build and deploy the site

Requires a self-hosted runner and repo secrets (DEPLOY_HOST, DEPLOY_USER,
DEPLOY_PATH, DEPLOY_SSH_KEY) to be set up before it will actually run.

.gitea/workflows/build-deploy.yml

@@ -0,0 +1,44 @@
+name: Build and deploy
+
+on:
+  push:
+    branches: [master]
+  workflow_dispatch: {}
+
+jobs:
+  build-and-deploy:
+    # Needs a self-hosted Gitea Actions runner with this label registered
+    # against git.haemka.in — none exists yet, set one up before enabling this.
+    runs-on: self-hosted
+    container: python:3.12-slim
+    steps:
+      - name: Install system dependencies
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends git rsync openssh-client
+
+      - name: Checkout (incl. theme submodule)
+        uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Install Python dependencies
+        run: pip install --no-cache-dir -r requirements.txt
+
+      - name: Build site
+        run: pelican -s publishconf.py
+
+      - name: Deploy via rsync
+        env:
+          DEPLOY_HOST: ${{ secrets.DEPLOY_HOST }}
+          DEPLOY_USER: ${{ secrets.DEPLOY_USER }}
+          DEPLOY_PATH: ${{ secrets.DEPLOY_PATH }}
+          DEPLOY_SSH_KEY: ${{ secrets.DEPLOY_SSH_KEY }}
+        run: |
+          mkdir -p ~/.ssh
+          printf '%s\n' "$DEPLOY_SSH_KEY" > ~/.ssh/deploy_key
+          chmod 600 ~/.ssh/deploy_key
+          ssh-keyscan -H "$DEPLOY_HOST" >> ~/.ssh/known_hosts 2>/dev/null
+          rsync -avz --delete \
+            -e "ssh -i ~/.ssh/deploy_key -o StrictHostKeyChecking=yes" \
+            output/ "${DEPLOY_USER}@${DEPLOY_HOST}:${DEPLOY_PATH}"