refactor(app): reshape session store reads around narrow hook surface

Eliminate sidebar re-render cascades by fixing both sides of the
subscription contract:

- Session-store writes preserve identity: setWorkspaces, mergeWorkspaces,
  removeWorkspace, and patchWorkspaceScripts return the previous Map/entry
  reference when content is unchanged.
- HostRuntimeController.updateSnapshot only notifies when a patched field
  actually changed; idle probe ticks no longer replace the snapshot.
- New canonical hook surface in stores/session-store-hooks.ts
  (useWorkspace, useWorkspaceFields, useWorkspaceStructure,
  useWorkspaceKeys, useResolveWorkspaceIdByCwd,
  useWorkspaceStatusesForBadges, useWorkspaceExecutionAuthority,
  useRecommendedProjectPaths, useHasWorkspaces). These are the only
  place to subscribe to workspaces.
- 15 greedy subscribers migrated to the hook surface. The sidebar is now
  driven by useWorkspaceStructure for identity/ordering; each row
  hydrates its own descriptor via useWorkspaceFields, so a workspace
  update re-renders only its row. Archive-redirect callbacks switched to
  event-time useSessionStore.getState().
- Deleted dead code: use-session-directory.ts, workspace-fetch-debug.ts,
  and the unused SidebarProjectEntry aggregates (activeCount,
  totalWorkspaces, aggregated statusBucket).

No user-visible behavior change. Targeted tests green (79 tests across
host-runtime, session-store, session-store-hooks, sidebar list, sidebar
row model, sidebar shortcuts, workspace source of truth).

packages/app/src/panels/terminal-panel.tsx

@@ -8,7 +8,7 @@ import { TerminalPane } from "@/components/terminal-pane";
 import { usePaneContext } from "@/panels/pane-context";
 import type { PanelDescriptor, PanelRegistration } from "@/panels/panel-registry";
 import { useSessionStore } from "@/stores/session-store";
-import { getWorkspaceExecutionAuthority } from "@/utils/workspace-execution";
+import { useWorkspaceExecutionAuthority } from "@/stores/session-store-hooks";
 
 type ListTerminalsPayload = ListTerminalsResponse["payload"];
 
@@ -25,11 +25,7 @@ function useTerminalPanelDescriptor(
   context: { serverId: string; workspaceId: string },
 ): PanelDescriptor {
   const client = useSessionStore((state) => state.sessions[context.serverId]?.client ?? null);
-  const workspaces = useSessionStore((state) => state.sessions[context.serverId]?.workspaces);
-  const workspaceAuthority = getWorkspaceExecutionAuthority({
-    workspaces,
-    workspaceId: context.workspaceId,
-  });
+  const workspaceAuthority = useWorkspaceExecutionAuthority(context.serverId, context.workspaceId)!;
   const workspaceDirectory = workspaceAuthority.ok
     ? workspaceAuthority.authority.workspaceDirectory
     : null;
@@ -63,8 +59,7 @@ function useTerminalPanelDescriptor(
 function TerminalPanel() {
   const isFocused = useIsFocused();
   const { serverId, workspaceId, target, isPaneFocused } = usePaneContext();
-  const workspaces = useSessionStore((state) => state.sessions[serverId]?.workspaces);
-  const workspaceAuthority = getWorkspaceExecutionAuthority({ workspaces, workspaceId });
+  const workspaceAuthority = useWorkspaceExecutionAuthority(serverId, workspaceId)!;
   const workspaceDirectory = workspaceAuthority.ok
     ? workspaceAuthority.authority.workspaceDirectory
     : null;