feat(ui): implement 'Twilight Velvet' dark theme and fix visibility issues

- Add 'Twilight Velvet' color palette to globals.css with OKLCH values
- Update SettingsPage headers, cards, and dialogs to use semantic theme variables
- Update HistoryCard, HistoryFeed, and DraftContent to support dark mode
- Update ProviderSelector and ProviderList to use custom card background (#2A2A3D)
- Add ThemeToggle component with improved visibility
- Ensure consistent use of 'bg-card', 'text-foreground', and 'text-muted-foreground'

tests/support/fixtures/index.ts

@@ -1,8 +1,12 @@
-import { test as base } from '@playwright/test';
-import { UserFactory } from './factories/user-factory';
+import { test as base, BrowserContext } from '@playwright/test';
+import { UserFactory } from '../factories/user.factory';
 
 type TestFixtures = {
     userFactory: UserFactory;
+    offlineControl: {
+        goOffline: (context: BrowserContext) => Promise<void>;
+        goOnline: (context: BrowserContext) => Promise<void>;
+    };
 };
 
 export const test = base.extend<TestFixtures>({
@@ -11,6 +15,24 @@ export const test = base.extend<TestFixtures>({
         await use(factory);
         await factory.cleanup();
     },
+    offlineControl: async ({ }, use) => {
+        const offlineFixture = {
+            goOffline: async (context: BrowserContext) => {
+                await context.setOffline(true);
+                for (const page of context.pages()) {
+                    // Dispatch event to simulate navigator.onLine behavior changes in app
+                    await page.evaluate(() => window.dispatchEvent(new Event('offline'))).catch(() => { });
+                }
+            },
+            goOnline: async (context: BrowserContext) => {
+                await context.setOffline(false);
+                for (const page of context.pages()) {
+                    await page.evaluate(() => window.dispatchEvent(new Event('online'))).catch(() => { });
+                }
+            },
+        };
+        await use(offlineFixture);
+    },
 });
 
 export { expect } from '@playwright/test';