Redesign dashboard with list layout, sparklines, and search

- Add sparkline component for 7-day price history visualization
- Convert product cards to horizontal list items
- Add search functionality to filter products by name/URL
- Backend returns sparkline data and 7-day price change with products
- Show price trend indicator (green for drops, red for increases)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/api/client.ts

@@ -41,6 +41,11 @@ export const authApi = {
 };
 
 // Products API
+export interface SparklinePoint {
+  price: number;
+  recorded_at: string;
+}
+
 export interface Product {
   id: number;
   user_id: number;
@@ -52,6 +57,8 @@ export interface Product {
   created_at: string;
   current_price: number | null;
   currency: string | null;
+  sparkline?: SparklinePoint[];
+  price_change_7d?: number | null;
 }
 
 export interface ProductWithStats extends Product {