ci: run workflows on the go-react runner image

The workflows used runs-on: ubuntu-latest, which mapped to
docker.gitea.com/runner-images:ubuntu-latest — an image whose Node from
setup-node won't execute (exit 127) and which lacks curl/jq. The runner
already advertises a purpose-built "go-react" CI image; point the
workflows at it instead.

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

.gitea/workflows/build-dev.yaml

@@ -13,7 +13,7 @@ env:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: go-react
     steps:
       - name: Checkout
         uses: actions/checkout@v4

.gitea/workflows/ci.yaml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   lint-and-typecheck:
-    runs-on: ubuntu-latest
+    runs-on: go-react
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
@@ -21,7 +21,7 @@ jobs:
 
   test:
     needs: lint-and-typecheck
-    runs-on: ubuntu-latest
+    runs-on: go-react
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
@@ -33,7 +33,7 @@ jobs:
 
   build:
     needs: test
-    runs-on: ubuntu-latest
+    runs-on: go-react
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
@@ -50,7 +50,7 @@ jobs:
 
   deploy:
     needs: build
-    runs-on: ubuntu-latest
+    runs-on: go-react
     if: github.ref == 'refs/heads/main' && github.event_name == 'push'
     environment: production
     steps: