ci(deploy): deploy to Render via deploy hook instead of Fly

- Replace Fly.io deploy step with a CI-gated Render deploy-hook trigger
  (uses RENDER_DEPLOY_HOOK_URL secret). render.yaml blueprint +
  render_entrypoint.sh already make the image Render-ready.
- Remove fly.toml (no longer deploying to Fly).

Author: obielin

.github/workflows/deploy.yml

@@ -12,12 +12,16 @@ jobs:
     needs: test
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v7
-
-      - name: Set up Flyctl
-        uses: superfly/flyctl-actions/setup-flyctl@master
-
-      - name: Deploy to Fly.io
+      - name: Trigger Render deploy
         env:
-          FLY_API_TOKEN: ${{ secrets.FLY_API_TOKEN }}
-        run: fly deploy --remote-only
+          RENDER_DEPLOY_HOOK_URL: ${{ secrets.RENDER_DEPLOY_HOOK_URL }}
+        run: |
+          if [ -z "$RENDER_DEPLOY_HOOK_URL" ]; then
+            echo "::error::RENDER_DEPLOY_HOOK_URL secret is not set." \
+                 "Add it under repo Settings > Secrets and variables > Actions" \
+                 "(get the URL from the Render service > Settings > Deploy Hook)."
+            exit 1
+          fi
+          echo "CI passed; triggering Render deploy..."
+          curl -fsS -X POST "$RENDER_DEPLOY_HOOK_URL"
+          echo "Render deploy triggered."