feat: add task comments feature with CRUD operations

- Introduced a new `task_comments` table in the database schema.
- Implemented task comments API endpoints for listing, creating, and deleting comments.
- Enhanced the task detail dialog to display comments and allow users to add new comments.
- Updated task row component to handle click events for viewing task details.
- Added a theme provider to manage light/dark mode across the application.
- Refactored Milkdown editor to use Crepe for improved markdown editing experience.
- Updated global styles to accommodate new editor and theme changes.
- Enhanced task filtering and sorting functionality in the tasks page.

src/main/ai/copilot.ts

@@ -0,0 +1,26 @@
+import { registerProvider, type AIProvider } from './provider';
+
+let token: string | null = null;
+
+const copilotProvider: AIProvider = {
+  name: 'copilot',
+  displayName: 'GitHub Copilot',
+
+  async initialize(t: string): Promise<boolean> {
+    token = t;
+    // Actual GitHub Copilot SDK client creation will be added in US-019.
+    // For now, having a token means the provider is ready.
+    return true;
+  },
+
+  isReady(): boolean {
+    return token !== null;
+  },
+};
+
+/** Get the raw Copilot token (used by future chat/completion calls). */
+export function getCopilotToken(): string | null {
+  return token;
+}
+
+registerProvider(copilotProvider);