ci(maestro): install node + pnpm for maestro-web build.rs

Compiling maestro-web now requires the frontend toolchain to build the
embedded SPA bundle.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -26,6 +26,13 @@ jobs:
                        --component rustfmt --component clippy
           echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
 
+      - name: Install Node.js + pnpm
+        run: |
+          curl -fsSL https://deb.nodesource.com/setup_20.x | bash -
+          apt-get install -y --no-install-recommends nodejs
+          corepack enable
+          corepack prepare pnpm@9.15.4 --activate
+
       - name: Cache cargo
         uses: actions/cache@v4
         with: