fix(2137): skip worktree isolation when .gitmodules detected (#2144)

* feat(sdk): add typed query foundation and gsd-sdk query (Phase 1)

Add sdk/src/query registry and handlers with tests, GSDQueryError, CLI query wiring, and supporting type/tool-scoping hooks. Update CHANGELOG. Vitest 4 constructor mock fixes in milestone-runner tests.

Made-with: Cursor

* fix(2137): skip worktree isolation when .gitmodules detected

When a project contains git submodules, worktree isolation cannot
correctly handle submodule commits — three separate gaps exist in
worktree setup, executor commit protocol, and merge-back. Rather
than patch each gap individually, detect .gitmodules at phase start
and fall back to sequential execution, which handles submodules
transparently (Option B).

Affected workflows: execute-phase.md, quick.md

---------

Co-authored-by: David Sienkowski <dave@sienkowski.com>

sdk/src/workstream-utils.ts

@@ -5,7 +5,7 @@
  * .planning/workstreams/<name>/ instead.
  */
 
-import { join } from 'node:path';
+import { posix } from 'node:path';
 
 /**
  * Validate a workstream name.
@@ -28,5 +28,6 @@ export function validateWorkstreamName(name: string): boolean {
  */
 export function relPlanningPath(workstream?: string): string {
   if (!workstream) return '.planning';
-  return join('.planning', 'workstreams', workstream);
+  // Use POSIX segments so the same logical path string is used on all platforms (Windows included).
+  return posix.join('.planning', 'workstreams', workstream);
 }