add auto-deploy workflow

hopefully it works. probably not knowing my luck

.github/workflows/deploy.yml

@@ -0,0 +1,24 @@
+name: Deploy
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  run_pull:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Set up SSH
+        run: |
+          install -m 600 -D /dev/null ~/.ssh/id_ed25519
+          echo "${{ secrets.SSH_PRIVATE_KEY }}" > ~/.ssh/id_ed25519
+          chmod 600 ~/.ssh/id_ed25519  # This should be redundant but seems to do the trick.
+          ssh-keyscan -H ${{ secrets.SSH_HOST }} > ~/.ssh/known_hosts
+
+      - name: Connect, pull, build and deploy
+        run: ssh ${{ secrets.SSH_USER }}@${{ secrets.SSH_HOST }} "cd ${{ secrets.WORK_DIR }} && git checkout ${{ secrets.MAIN_BRANCH }} && git pull && yarn build && exit"
+
+      - name: Clean up
+        run: rm -rf ~/.ssh