fix: use setItem helper and safer Playwright selector in tests

- Replace direct localStorage.setItem() with setItem helper in use-settings-migration.ts (line 472) for consistent storage-availability checks and error handling
- Replace brittle attribute selector with Playwright's getByRole in open-existing-project.spec.ts (line 162) to handle names containing special characters

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

test/agent-session-test-115699-vyk2nk2/test-project-1768743000887/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "test-project-1768743000887",
+  "version": "1.0.0"
+}

test/feature-backlog-test-114171-aysp86y/test-project-1768742910934/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "test-project-1768742910934",
+  "version": "1.0.0"
+}