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/hooks/use-pr-pane-data.ts

@@ -7,9 +7,6 @@ import type {
 import { mapPrPaneData, type PrPaneData } from "../utils/pr-pane-data";
 import { useCheckoutPrStatusQuery } from "./use-checkout-pr-status-query";
 
-const PR_PANE_TIMELINE_STALE_TIME = 15_000;
-const PR_PANE_TIMELINE_REFETCH_INTERVAL = 30_000;
-
 type CheckoutPrStatusPayloadError = CheckoutPrStatusResponse["payload"]["error"];
 type PullRequestTimeline = PullRequestTimelineResponse["payload"];
 
@@ -81,8 +78,10 @@ export function usePrPaneData({
       }
     },
     enabled: shouldFetchTimeline,
-    staleTime: PR_PANE_TIMELINE_STALE_TIME,
-    refetchInterval: PR_PANE_TIMELINE_REFETCH_INTERVAL,
+    staleTime: Infinity,
+    refetchOnMount: false,
+    refetchOnReconnect: false,
+    refetchOnWindowFocus: false,
     placeholderData: keepPreviousData,
     retry: (failureCount, error) => !isUnsupportedTimelineError(error) && failureCount < 3,
   });