fix(tests): use cross-platform path split in run-manager timestamp test

The test split on "/" which fails on Windows where paths use "\".

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/resources/extensions/gsd/tests/run-manager.test.ts

@@ -156,9 +156,8 @@ describe("createRun", () => {
 
     const runDir = createRun(base, "test-workflow");
 
-    // Extract the timestamp directory name
-    const parts = runDir.split("/");
-    const timestamp = parts[parts.length - 1];
+    // Extract the timestamp directory name (use path.sep for cross-platform)
+    const timestamp = runDir.split(/[/\\]/).pop()!;
 
     // Should not contain colons (filesystem-unsafe on Windows)
     assert.ok(!timestamp.includes(":"), `timestamp should not contain colons: ${timestamp}`);