Prevent auto-reloading diff views when status area shifts (#5951)

* Avoid auto-reloading single-file diff tabs if their status row has
  moved to a different area (e.g. from unstaged to staged).
* Prevent auto-reloading combined uncommitted diffs when they are
  backed by an uncommitted entries snapshot.
* This preserves the open tab's original diff context as staging and
  commit status changes, preventing useful context from being lost.

src/main/runtime/headless-tab-group-split-layout.ts

@@ -193,8 +193,7 @@ export function buildHeadlessTabGroupSplit(args: {
       return {
         ...group,
         tabOrder: sourceOrder,
-        activeTabId:
-          group.activeTabId === args.tabId ? (sourceOrder[0] ?? null) : group.activeTabId
+        activeTabId: group.activeTabId === args.tabId ? (sourceOrder[0] ?? null) : group.activeTabId
       }
     }
     return group