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/factories/settings.factory.ts

@@ -0,0 +1,20 @@
+import { faker } from '@faker-js/faker';
+
+export interface UserSettings {
+    theme: 'light' | 'dark' | 'system';
+    fontSize: number;
+    reduceMotion: boolean;
+    language: string;
+    notificationsEnabled: boolean;
+}
+
+export const createSettings = (overrides: Partial<UserSettings> = {}): UserSettings => {
+    return {
+        theme: faker.helpers.arrayElement(['light', 'dark', 'system']),
+        fontSize: faker.number.int({ min: 12, max: 24 }),
+        reduceMotion: faker.datatype.boolean(),
+        language: 'en-US',
+        notificationsEnabled: faker.datatype.boolean(),
+        ...overrides,
+    };
+};

tests/support/factories/user.factory.ts

@@ -0,0 +1,37 @@
+import { faker } from '@faker-js/faker';
+
+/**
+ * UserFactory
+ * 
+ * Handles creation and cleanup of test users.
+ * Note: Since this is a local-first app without a real backend API for user creation yet,
+ * this factory currently generates mock data. adapting to real API calls later.
+ */
+export class UserFactory {
+    // In a real app, we would track IDs here for cleanup
+    // private createdUserIds: string[] = [];
+
+    async createUser(overrides = {}) {
+        const user = {
+            id: faker.string.uuid(),
+            email: faker.internet.email(),
+            name: faker.person.fullName(),
+            password: faker.internet.password(),
+            createdAt: new Date().toISOString(),
+            ...overrides,
+        };
+
+        // Placeholder: In a real app, you would POST to API here
+        // const response = await fetch(\`\${process.env.API_URL}/users\`, ...);
+
+        return user;
+    }
+
+    async cleanup() {
+        // Placeholder: In a real app, you would DELETE users here
+        // for (const id of this.createdUserIds) { ... }
+
+        // For now, no cleanup needed for transient mock data
+        return Promise.resolve();
+    }
+}