feat(server,app): redesign git/GitHub refresh architecture with server authority

Centralizes refresh orchestration in WorkspaceGitService and GitHubService:
server coalesces, deduplicates, and throttles git/GitHub reads; clients peek
snapshots (cold reads fall through to a one-shot fetch) and never drive
refreshes. Introduces a two-TTL model (consumer vs internal), force-emit
bypass so fingerprint-matched refreshes still propagate, notifyGitMutation
wiring at ~13 action handlers, adaptive GitHub polling based on check state,
and checkout_status_update / prStatus push-to-cache wire messages. Fixes the
stale diff-stat bug and the inverted base-branch diff direction, and flips
next-action affordances promptly after commit / PR merge.

packages/app/src/screens/new-workspace-screen.tsx

@@ -162,6 +162,10 @@ export function NewWorkspaceScreen({
       return connectedClient.getCheckoutStatus(sourceDirectory);
     },
     enabled: isConnected && !!client,
+    staleTime: Infinity,
+    refetchOnMount: false,
+    refetchOnReconnect: false,
+    refetchOnWindowFocus: false,
   });
 
   const currentBranch = checkoutStatusQuery.data?.currentBranch ?? null;