test: unblock vitest 5 (localStorage accessor, hoisted vi.mock)

Two independent breakages from the vitest 4.1.11 -> 5.0.0 bump:

1. vitest 5 no longer shadows the jsdom window globals with writable ones, so
   `global.localStorage = ...` hits jsdom's getter-only accessor and throws
   "Cannot set property localStorage of [object Window] which has only a
   getter". test/setup.ts is a setup file, so both test files failed to
   collect. Object.defineProperty replaces the accessor outright.

2. vitest 5 rejects a vi.mock() call outside module top level instead of
   silently hoisting it. The call sat inside beforeEach, which was already
   misleading -- it is hoisted above the imports and its factory runs once, on
   first import of the mocked module, so it was never re-applied per test.
   Moved to top level, where it actually executes; the beforeEach keeps its
   resetModules/mockClear.

Verified against both vitest 4.1.11 and 5.0.0: 2 files / 9 tests pass on each.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T2BPPeWMdYEmYbN6eGCBSg

test/setup.ts

@@ -31,7 +31,15 @@ class LocalStorageMock {
   }
 }
 
-global.localStorage = new LocalStorageMock() as unknown as Storage
+// jsdom defines localStorage as a getter-only accessor on the window object, so a
+// plain assignment throws ("Cannot set property localStorage ... which has only a
+// getter") under vitest 5, which no longer shadows it with a writable global.
+// defineProperty replaces the accessor outright and works on both.
+Object.defineProperty(globalThis, 'localStorage', {
+  value: new LocalStorageMock() as unknown as Storage,
+  writable: true,
+  configurable: true,
+})
 
 // Make Vue composables globally available
 global.ref = Vue.ref