fix(sessions): keep missing-worktree relocation manual

Remove automatic moves on session activation, terminal failures, and archive restoration while preserving manual moves and worktree deletion.

Replace directory listing probes with a stat-only endpoint using Node built-ins, including an isolated module-load regression test for packaged desktop.

Validation: focused session, worktree, filesystem, localization, and bridge tests; workspace type-check and lint; web and VS Code builds. Desktop startup and behavior verified by the maintainer.

packages/ui/src/sync/__tests__/issue-2039.test.ts

@@ -309,7 +309,6 @@ mock.module("../session-actions", () => ({
   unrevertSession: mock(async () => undefined),
   forkFromMessage: mock(async () => undefined),
   fetchMessagesForSession: mock(async () => undefined),
-  relocateSessionFromMissingDirectory: mock(async () => ({ status: "unchanged" })),
   getSessionLastAssistantModel: () => null,
   patchSessionMetadata: mock(async () => undefined),
   abortCurrentOperation: mock(async () => undefined),