CUB-CI: Consolidate CI — switch to ubuntu-latest with manual Go/Node install

- Remove custom go-react runner label (was inconsistent on PR branches)
- Replace with ubuntu-latest + manual Go 1.23 / Node 22 install
  (actions/setup-go and setup-node don't work with Gitea Act runner)
- Remove duplicate build-dev.yaml workflow (already deleted)
- All steps: Go test → Go build → npm ci → npm lint → npm build
- Docker push on push events only (unchanged)

.gitea/workflows/dev.yml

@@ -7,17 +7,29 @@ on:
     branches: [dev]
 
 env:
+  GO_VERSION: "1.23"
+  NODE_VERSION: "22"
   REGISTRY: code.cubecraftcreations.com
   BACKEND_IMAGE: ${{ gitea.repository }}/backend
   FRONTEND_IMAGE: ${{ gitea.repository }}/frontend
 
 jobs:
   test-and-build:
-    runs-on: go-react
+    runs-on: ubuntu-latest
 
     steps:
       - uses: actions/checkout@v4
 
+      - name: Install Go
+        run: |
+          curl -fsSL "https://go.dev/dl/go${GO_VERSION}.linux-amd64.tar.gz" | sudo tar -C /usr/local -xz
+          echo "/usr/local/go/bin" >> $GITHUB_PATH
+
+      - name: Install Node.js
+        run: |
+          curl -fsSL "https://nodejs.org/dist/v${NODE_VERSION}/node-v${NODE_VERSION}-linux-x64.tar.xz" | sudo tar -C /usr/local --strip-components=1 -xJ
+          echo "/usr/local/bin" >> $GITHUB_PATH
+
       - name: Run backend tests
         run: go test ./...
         working-directory: ./go-backend
@@ -41,7 +53,7 @@ jobs:
   docker-build-push:
     needs: test-and-build
     if: gitea.event_name == 'push'
-    runs-on: go-react
+    runs-on: ubuntu-latest
 
     steps:
       - uses: actions/checkout@v4