Add blog template, build script and CI workflow

.gitea/workflows/build.yml

@@ -0,0 +1,27 @@
+# Rebuilds pascal-maas.nl on every push to main.
+# Runs on the self-hosted runner next to Gitea; /srv/site is what nginx serves.
+name: Build blog
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: linux
+    defaults:
+      run:
+        shell: sh
+    steps:
+      - name: Fetch source
+        run: |
+          rm -rf src
+          git clone --depth 1 --branch "${{ gitea.ref_name }}" \
+            "https://oauth2:${{ gitea.token }}@git.pascal-maas.nl/${{ gitea.repository }}.git" src
+
+      - name: Build
+        run: python3 src/build.py src out
+
+      - name: Publish
+        run: rsync -a --delete out/ /srv/site/