Isolate branch switcher query from WorkspaceScreenContent to prevent 20ms re-renders

Move useBranchSwitcher into BranchSwitcher component so query state
changes only re-render the small header widget instead of the entire
workspace screen. Also memo-wrap AgentStatusBar to skip re-renders
on keystroke.

packages/server/src/server/session.ts

@@ -5876,7 +5876,11 @@ export class Session {
       };
 
       const lastEmitted = subscription.lastEmittedByWorkspaceId.get(workspaceId);
-      if (lastEmitted && lastEmitted.kind === "upsert" && equal(lastEmitted.workspace, nextWorkspace)) {
+      if (
+        lastEmitted &&
+        lastEmitted.kind === "upsert" &&
+        equal(lastEmitted.workspace, nextWorkspace)
+      ) {
         continue;
       }