ci: fix submodule auth + replace matrix build for device-agent

- persist-credentials: false on all workflows (prevent Gitea overwriting insteadOf URL)
- Replace matrix strategy in build_device_agent.yaml with sequential builds (act_runner v0.6.1 ParallelExecutor crash)
- Build all 3 platforms (linux/amd64, linux/arm64, windows/amd64) in single step

.gitea/workflows/build_dashboard.yaml

@@ -15,7 +15,7 @@ jobs:
           submodules: true
           fetch-depth: 0
           token: ${{ secrets.BUILD_TOKEN }}
-          persist-credentials: true
+          persist-credentials: false
 
       - uses: actions/setup-node@v4
         with: