ci: add auto-rebase and conflict detection workflows (#6578)

* ci: add auto-rebase and conflict detection workflows

- Add auto-rebase.yml: automatically rebases all open PRs onto latest
  master on every push, using peter-evans/rebase@v4
- Add conflict-check.yml: labels conflicting PRs with 'needs-rebase'
  and comments with rebase instructions, using
  eps1lon/actions-label-merge-conflict@v3
- Update PR template: add 'Allow edits from maintainers' checkbox
- Update CONTRIBUTING.md: add 'Keeping Your PR Up-to-Date' section
  with rebase instructions and upstream setup guide

* docs: clarify that 'Allow edits from maintainers' only affects the PR branch

---------

Co-authored-by: Ashutosh Kumar <ashutoshx7@users.noreply.github.com>

Author: Ashutoshx7

.github/PULL_REQUEST_TEMPLATE/generic.md

@@ -56,6 +56,7 @@ This PR fixes #
 -   [ ] I have followed the project's coding style guidelines.
 -   [ ] I have run `npm run lint` and `npx prettier --check .` with no errors.
 -   [ ] I have addressed the code review feedback from the previous submission, if applicable.
+-   [ ] I have enabled **"Allow edits from maintainers"** _(required for auto-rebase; this only affects the PR branch, not your fork)_.
 
 ## Additional Notes for Reviewers
 

.github/workflows/auto-rebase.yml

@@ -0,0 +1,24 @@
+name: Auto Rebase PRs
+
+on:
+    push:
+        branches: [master]
+    workflow_dispatch:
+
+permissions:
+    contents: write
+    pull-requests: write
+
+jobs:
+    rebase:
+        name: Auto-rebase all open PRs onto latest master
+        runs-on: ubuntu-latest
+        steps:
+            - uses: peter-evans/rebase@v4
+              with:
+                  base: master
+                  exclude-labels: |
+                      no-rebase
+                      wip
+                      do-not-merge
+                  exclude-drafts: true

.github/workflows/conflict-check.yml

@@ -0,0 +1,43 @@
+name: Label Conflicting PRs
+
+on:
+    push:
+        branches: [master]
+    pull_request_target:
+        types: [synchronize]
+
+permissions:
+    contents: read
+    pull-requests: write
+
+jobs:
+    check:
+        name: Detect merge conflicts
+        runs-on: ubuntu-latest
+        steps:
+            - uses: eps1lon/actions-label-merge-conflict@v3
+              with:
+                  dirtyLabel: "needs-rebase"
+                  repoToken: "${{ secrets.GITHUB_TOKEN }}"
+                  retryAfter: 120
+                  retryMax: 5
+                  continueOnMissingPermissions: true
+                  commentOnDirty: |
+                      **This PR has merge conflicts with `master`.**
+
+                      Please rebase your branch:
+                      ```bash
+                      # Add upstream remote (one-time setup)
+                      git remote add upstream https://github.com/sugarlabs/musicblocks.git
+
+                      # Fetch latest master and rebase
+                      git fetch upstream
+                      git rebase upstream/master
+
+                      # Resolve any conflicts, then:
+                      git push --force-with-lease origin YOUR_BRANCH
+                      ```
+
+                      > **Tip:** Enable "Allow edits from maintainers" on this PR so we can auto-rebase for you next time. This only grants access to your PR branch. Your fork's other branches are not affected.
+                  commentOnClean: |
+                      Merge conflicts resolved. Ready for review.

CONTRIBUTING.md

@@ -160,6 +160,43 @@ Follow these steps when contributing:
 
 7.  Respond to review feedback and update your branch as needed.
 
+### Keeping Your PR Up-to-Date
+
+Our CI automatically rebases your PR onto the latest `master` whenever
+new changes are merged. For this to work on fork PRs, you **must** enable
+**"Allow edits from maintainers"** when creating your PR.
+
+> **Note:** This checkbox only grants maintainers push access to the
+> _specific branch_ associated with your PR. It does **not** affect
+> your fork's other branches or settings.
+
+If your PR develops merge conflicts that can't be auto-resolved, our bot
+will label it with `needs-rebase` and comment with step-by-step rebase
+instructions.
+
+**Manual rebase (if needed):**
+
+```bash
+# Add the upstream remote (one-time setup)
+git remote add upstream https://github.com/sugarlabs/musicblocks.git
+
+# Fetch the latest changes and rebase
+git fetch upstream
+git rebase upstream/master
+
+# Resolve any conflicts in your editor, then:
+git add .
+git rebase --continue
+
+# Push the updated branch
+git push --force-with-lease origin your-branch-name
+```
+
+> **Tip:** Enable **"Allow edits from maintainers"** on your PR so
+> maintainers and our automation can keep your branch current. This
+> setting only applies to the PR branch. Your other branches and
+> fork settings are not affected.
+
 ### After your PR is merged
 
 Please note that production deployments of Music Blocks are **manual**.