feat: widget has two tap targets — fitness + add food

Widget background tap → platform://fitness → opens Fitness tab
Widget + button tap → platform://add-food → opens Fitness + food assistant

Small widget: + button in bottom-right corner (emerald green)
Medium widget: + button in bottom-right corner
Lock screen widgets: single tap → fitness (no room for + button)

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

ios/Platform/Platform/ContentView.swift

@@ -121,9 +121,15 @@ struct MainTabView: View {
             AssistantSheetView(onFoodAdded: foodAdded)
         }
         .onOpenURL { url in
-            if url.scheme == "platform" && url.host == "add-food" {
-                selectedTab = 1 // Fitness tab
+            guard url.scheme == "platform" else { return }
+            switch url.host {
+            case "fitness":
+                selectedTab = 1
+            case "add-food":
+                selectedTab = 1
                 showAssistant = true
+            default:
+                break
             }
         }
         .task {