feat: Add a Forgejo Actions pipeline

Added a Forgejo Actions CI/CD pipeline to supersede the manual deploy.sh,
automating builds and deployments on push.

.forgejo/workflows/deploy.yaml

@@ -0,0 +1,17 @@
+name: Build and Deploy
+
+on:
+  push:
+    branches:
+      - master
+      - develop
+
+jobs:
+  deploy:
+    runs-on: self-hosted
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Deploy
+        run: nix shell nixpkgs#mdbook --command ./deploy.sh local