fix: match mockup container width — layout main uncapped to 1380px, remove padding conflict

Dashboard surface now renders at 1280px matching the React mockup exactly.
All 9 pages verified: zero mobile overflow.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend-v2/src/routes/(app)/+layout.svelte

@@ -45,16 +45,16 @@
 	}
 	main {
 		flex: 1;
-		padding: 16px;
+		padding: 0 16px;
 		width: 100%;
-		max-width: 640px;
+		max-width: 100%;
 		margin: 0 auto;
 	}
 
 	@media (min-width: 768px) {
 		main {
-			padding: 20px;
-			max-width: 1200px;
+			padding: 0;
+			max-width: 1380px;
 		}
 	}
 </style>