ci: fix fork sync auth and add manual trigger

The actions/checkout step persisted the default GITHUB_TOKEN auth header,
which overrode the FORK_SYNC_TOKEN PAT embedded in the fork URL and caused
the push to the private deployment fork to fail with "Repository not found".
Set persist-credentials: false so the PAT is used. Also add workflow_dispatch
so the sync can be triggered manually.

Author: junaiddshaukat

.github/workflows/sync-fork.yml

@@ -4,6 +4,7 @@ name: Sync Fork & Deploy
 on:
   push:
     branches: [main]
+  workflow_dispatch:
 
 jobs:
   sync-fork:
@@ -17,6 +18,9 @@ jobs:
         uses: actions/checkout@v4
         with:
           fetch-depth: 0
+          # Don't leave the default GITHUB_TOKEN auth header configured,
+          # otherwise it overrides the PAT below when pushing to the fork.
+          persist-credentials: false
 
       - name: Push to fork
         run: |