FN-5877: add sync-with-origin remotes action

Add a one-click Remotes sync flow that rebases on pull before pushing.

- add a Sync button in Git Manager Remotes that runs pull --rebase and then push
- stop before pushing when the rebase pull reports a conflict or fails, and surface toasts/status updates
- cover successful, conflicting, failing, and loading sync behavior in GitManagerModal tests
- document the new Sync action in the dashboard guide

Files changed:
 docs/dashboard-guide.md                            |   1 +
 .../dashboard/app/components/GitManagerModal.tsx   |  39 ++++++++
 .../components/__tests__/GitManagerModal.test.tsx  | 100 +++++++++++++++++++++
 3 files changed, 140 insertions(+)

Fusion-Task-Id: FN-5877

Fusion-Task-Lineage: 2e28c00d-b965-4f44-a6fa-26536d91d16d

packages/dashboard/app/components/GitManagerModal.tsx

@@ -818,6 +818,28 @@ export function GitManagerModal({ isOpen, onClose, tasks: _tasks, addToast, proj
     }
   }, [addToast, projectId]);
 
+  const handleSyncWithOrigin = useCallback(async () => {
+    setRemoteLoading("sync");
+    try {
+      const pullResult = await pullBranch({ rebase: true }, projectId);
+      setLastRemoteResult(pullResult);
+      if (pullResult.conflict) {
+        addToast("Merge conflict detected. Resolve manually.", "error");
+        return;
+      }
+
+      const pushResult = await pushBranch(projectId);
+      setLastRemoteResult(pushResult);
+      addToast("Synced with origin (pull --rebase + push)", "success");
+      const statusData = await fetchGitStatus(projectId, { extended: true });
+      setStatus(statusData);
+    } catch (err) {
+      addToast(getErrorMessage(err) || "Sync with origin failed", "error");
+    } finally {
+      setRemoteLoading(null);
+    }
+  }, [addToast, projectId]);
+
   // Fetch rootDir from config (used as worktreePath for the per-task sync
   // button surfaced from RemotesPanel below).
   useEffect(() => {
@@ -1039,6 +1061,7 @@ export function GitManagerModal({ isOpen, onClose, tasks: _tasks, addToast, proj
                 onFetch={handleFetch}
                 onPull={handlePull}
                 onPush={handlePush}
+                onSync={handleSyncWithOrigin}
                 onSyncIntegrationTip={handleSyncIntegrationTip}
                 syncIntegrationDisabled={
                   !status?.integrationBranch ||
@@ -2244,6 +2267,7 @@ function RemotesPanel({
   onFetch,
   onPull,
   onPush,
+  onSync,
   onSyncIntegrationTip,
   syncIntegrationDisabled,
   addToast,
@@ -2256,6 +2280,7 @@ function RemotesPanel({
   onFetch: () => void;
   onPull: (options?: { rebase?: boolean }) => void;
   onPush: () => void;
+  onSync: () => void;
   onSyncIntegrationTip: () => void;
   syncIntegrationDisabled: boolean;
   addToast: (message: string, type?: ToastType) => void;
@@ -2761,6 +2786,20 @@ function RemotesPanel({
                     )}
                     Push
                   </button>
+                  <button
+                    className="btn btn-primary"
+                    onClick={onSync}
+                    disabled={remoteLoading !== null || loading}
+                    title="Pull --rebase from origin, then push current branch"
+                    data-testid="remotes-sync-origin-btn"
+                  >
+                    {remoteLoading === "sync" ? (
+                      <Loader2 size={14} className="spin" />
+                    ) : (
+                      <GitMerge size={14} />
+                    )}
+                    Sync
+                  </button>
                   {status?.integrationBranch && (
                     <button
                       className="btn gm-sync-integration-btn"