ci: install Go via setup-go (go-react image has Node but not Go)

build-dev failed with "go: command not found" — the go-react image ships
Node but no Go. Restore setup-go (its static Go binary runs on this runner,
unlike setup-node's dynamic Node), and keep Node from the image.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/build-dev.yaml

@@ -16,8 +16,14 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      # The go-react image ships Go + Node, so no setup-go/setup-node:
-      # those download tool-cache binaries that don't run on this runner.
+      # go-react has Node but not Go. setup-go installs a statically-linked
+      # Go that runs fine here; setup-node's dynamically-linked Node does
+      # not (so Node comes from the image instead).
+      - name: Setup Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: "1.25"
+
       - name: Toolchain versions
         run: |
           go version