fix(migration): normalize legacy theme values under v5 marker

Two related bugs surfaced during end-to-end verification:

1. The 'isAlreadyV5' short-circuit in both the main-side and renderer-side
   v4-to-v5 transforms returned the persisted object as-is when a
   migration.version=5 marker was present. A previously-shipped v4 build
   had written theme: 'ayu-light' (and similar) under the v5 marker;
   the transform trusted the marker and passed the invalid theme through,
   which then failed the renderer's zod schema on every launch and
   reset user settings to defaults.

   Fix: in both transforms, when isAlreadyV5 matches, normalize theme
   against the v5 enum (light/dark/system) and validate the full result
   with the v5 schema before returning. Out-of-range values are replaced
   with the v5 default ('system').

2. The renderer's settings-store onRehydrateStorage callback called
   useSettingsStore.setState() to reset the store on validation failure.
   At that moment the store is still being constructed, and setState
   could hit a TDZ ReferenceError (the one we already wrapped in a
   try/catch in v5.0.0, which only hid the symptom).

   Fix: return the normalized state object from onRehydrateStorage
   instead. Zustand's persist middleware applies the returned value
   *after* construction completes, so there is no TDZ.

Tests: 334 vitest + 208 jest = 542 passing.
E2E: 12/12 verify-features.mjs steps green; no console errors.

Amit Haridas

tests/unit/lib/migrations/v4-to-v5.test.ts

@@ -26,6 +26,16 @@ describe('migrateV4ToV5', () => {
     expect(a).toEqual(b);
   });
 
+  test('normalizes legacy theme names like "ayu-light" to a v5 value', () => {
+    // A previously-shipped v4 build wrote theme: 'ayu-light' (and similar).
+    // When an already-v5-marker file has such a value, isAlreadyV5 used to
+    // short-circuit and return the file as-is — which then failed the v5
+    // schema and reset user settings on every launch. The transform must
+    // normalize unknown theme values to the schema's default.
+    const out = migrateV4ToV5({ 'migration.version': 5, theme: 'ayu-light' });
+    expect(['light', 'dark', 'system']).toContain(out.theme);
+  });
+
   test('exposes the v4 schema for use by main', () => {
     expect(v4SettingsSchema).toBeDefined();
   });