Fix: grant push permissions to social cache workflow

Checkout with DASHBOARD_GITHUB_TOKEN PAT so git push succeeds.
Also add explicit contents: write permission at workflow level.
Fixes 403 'Permission denied to github-actions[bot]' error.

.github/workflows/update-social-cache.yml

@@ -12,12 +12,17 @@ on:
         default: 'false'
         type: boolean
 
+permissions:
+  contents: write
+
 jobs:
   update:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          token: ${{ secrets.DASHBOARD_GITHUB_TOKEN }}
 
       - name: Setup Node.js
         uses: actions/setup-node@v4