ci: Auto-merge PRs from fieldmate releases

This commit introduces a GitHub Actions workflow that automatically merges pull requests created by the fieldmate release process.

What it does:
- Detects PRs from branches starting with `fieldmate-auto-release`
- Attempts to enable auto-merge via GitHub CLI
- Falls back to direct squash merge if auto-merge is not possible
- Uses consistent commit messages and descriptions

This ensures that updates to fieldmate in frappe_docker are propagated cleanly and automatically, triggering rebuilds where needed.

.github/workflows/auto-merge-fieldmate.yml

@@ -0,0 +1,42 @@
+name: Auto-merge PRs from fieldmate
+
+on:
+  pull_request:
+    branches:
+      - main
+    types:
+      - opened
+      - synchronize
+      - reopened
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  automerge:
+    if: startsWith(github.head_ref, 'fieldmate-auto-release')
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Enable auto-merge or fallback merge
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+        run: |
+          echo "Trying to enable auto-merge for PR #$PR_NUMBER"
+
+          # Try auto-merge first
+          gh pr merge "$PR_NUMBER" \
+            --squash \
+            --auto \
+            --delete-branch \
+            --body "$COMMIT_BODY" \
+            --subject "$COMMIT_TITLE" || \
+
+          # Fallback: direct squash merge
+          gh pr merge "$PR_NUMBER" \
+            --squash \
+            --delete-branch \
+            --body "$COMMIT_BODY" \
+            --subject "$COMMIT_TITLE"