ci(docs+tests) Bootstrap pnpm + Node for sphinx-vite-builder source build

why: While gp-sphinx-family deps resolve from the
improved-defaults-reprs branch via [tool.uv.sources], uv builds
gp-furo-theme from source — its PEP 517 backend is
sphinx-vite-builder, which runs pnpm install + vite build at install
time. CI runners have no pnpm/Node, so the install fails. Revert
this and the uv.sources block once gp-sphinx>=0.0.1a18 publishes.

what:
- tests.yml: add pnpm/action-setup@v6 + setup-node@v6 before each
  uv sync step (build job, release job)
- docs.yml: same, gated on env.PUBLISH == 'true' to mirror the
  surrounding steps

Author: tony

.github/workflows/docs.yml

@@ -51,6 +51,22 @@ jobs:
         if: env.PUBLISH == 'true'
         run: uv python install ${{ matrix.python-version }}
 
+      # [DO NOT MERGE] pnpm + Node bootstrap for sphinx-vite-builder source build
+      # of gp-furo-theme — required while gp-sphinx-family deps resolve from the
+      # improved-defaults-reprs branch (see [tool.uv.sources]). Revert with the
+      # uv.sources block when gp-sphinx>=0.0.1a18 lands.
+      - name: Install pnpm
+        if: env.PUBLISH == 'true'
+        uses: pnpm/action-setup@v6
+        with:
+          version: 10
+      - name: Set up Node
+        if: env.PUBLISH == 'true'
+        uses: actions/setup-node@v6
+        with:
+          node-version: 22
+          cache: pnpm
+
       - name: Install dependencies [w/ docs]
         if: env.PUBLISH == 'true'
         run: uv sync --all-extras --dev

.github/workflows/tests.yml

@@ -33,6 +33,20 @@ jobs:
           print("libtmux Server:", server)
           '
 
+      # [DO NOT MERGE] pnpm + Node bootstrap for sphinx-vite-builder source build
+      # of gp-furo-theme — required while gp-sphinx-family deps resolve from the
+      # improved-defaults-reprs branch (see [tool.uv.sources]). Revert with the
+      # uv.sources block when gp-sphinx>=0.0.1a18 lands.
+      - name: Install pnpm
+        uses: pnpm/action-setup@v6
+        with:
+          version: 10
+      - name: Set up Node
+        uses: actions/setup-node@v6
+        with:
+          node-version: 22
+          cache: pnpm
+
       - name: Install dependencies
         run: uv sync --all-extras --dev
 
@@ -111,6 +125,20 @@ jobs:
       - name: Set up Python ${{ matrix.python-version }}
         run: uv python install ${{ matrix.python-version }}
 
+      # [DO NOT MERGE] pnpm + Node bootstrap for sphinx-vite-builder source build
+      # of gp-furo-theme — required while gp-sphinx-family deps resolve from the
+      # improved-defaults-reprs branch (see [tool.uv.sources]). Revert with the
+      # uv.sources block when gp-sphinx>=0.0.1a18 lands.
+      - name: Install pnpm
+        uses: pnpm/action-setup@v6
+        with:
+          version: 10
+      - name: Set up Node
+        uses: actions/setup-node@v6
+        with:
+          node-version: 22
+          cache: pnpm
+
       - name: Install dependencies
         run: uv sync --all-extras --dev