fix: warm sheet header, welcome state for AI chat, consistent colors

- Custom sheet header with warm canvas background (no white bar)
- Tab picker styled as warm pills (not default segmented control)
- AI Chat welcome state: sparkles icon + 'What did you eat?' prompt
- All backgrounds use canvas color consistently

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

ios/Platform/Platform/ContentView.swift

@@ -63,28 +63,62 @@ struct MainTabView: View {
 }
 
 struct AssistantSheetView: View {
+    @Environment(\.dismiss) private var dismiss
     @State private var selectedMode = 0
 
     var body: some View {
-        NavigationStack {
         VStack(spacing: 0) {
-                Picker("Mode", selection: $selectedMode) {
-                    Text("AI Chat").tag(0)
-                    Text("Quick Add").tag(1)
-                }
-                .pickerStyle(.segmented)
-                .padding(.horizontal)
+            // Custom header — warm background
+            VStack(spacing: 12) {
+                // Drag handle
+                Capsule()
+                    .fill(Color.textTertiary.opacity(0.3))
+                    .frame(width: 36, height: 5)
                     .padding(.top, 8)
 
+                Text("Add Food")
+                    .font(.headline)
+                    .foregroundStyle(Color.textPrimary)
+
+                // Tab picker — warm styled
+                HStack(spacing: 4) {
+                    tabButton("AI Chat", icon: "sparkles", index: 0)
+                    tabButton("Quick Add", icon: "magnifyingglass", index: 1)
+                }
+                .padding(4)
+                .background(Color.textTertiary.opacity(0.08))
+                .clipShape(Capsule())
+                .padding(.horizontal, 40)
+            }
+            .padding(.bottom, 12)
+            .background(Color.canvas)
+
+            // Content
             if selectedMode == 0 {
                 AssistantChatView()
             } else {
                 FoodSearchView(isSheet: true)
             }
         }
-            .navigationTitle("Add Food")
-            .navigationBarTitleDisplayMode(.inline)
-        }
+        .background(Color.canvas)
         .presentationDetents([.large])
     }
+
+    private func tabButton(_ title: String, icon: String, index: Int) -> some View {
+        Button {
+            withAnimation(.easeInOut(duration: 0.2)) { selectedMode = index }
+        } label: {
+            HStack(spacing: 5) {
+                Image(systemName: icon)
+                    .font(.caption2)
+                Text(title)
+                    .font(.subheadline.weight(selectedMode == index ? .semibold : .regular))
+            }
+            .foregroundStyle(selectedMode == index ? Color.textPrimary : Color.textTertiary)
+            .padding(.horizontal, 16)
+            .padding(.vertical, 8)
+            .background(selectedMode == index ? Color.surfaceCard : Color.clear)
+            .clipShape(Capsule())
+        }
+    }
 }

ios/Platform/Platform/Features/Assistant/AssistantChatView.swift

@@ -10,6 +10,27 @@ struct AssistantChatView: View {
             ScrollViewReader { proxy in
                 ScrollView {
                     LazyVStack(spacing: 8) {
+                        // Welcome state when no messages
+                        if vm.messages.isEmpty {
+                            VStack(spacing: 16) {
+                                Spacer(minLength: 60)
+                                Image(systemName: "sparkles")
+                                    .font(.system(size: 40))
+                                    .foregroundStyle(Color.accentWarm.opacity(0.4))
+                                Text("What did you eat?")
+                                    .font(.title3.weight(.semibold))
+                                    .foregroundStyle(Color.textPrimary)
+                                Text("Describe your food naturally.\n\"2 eggs and toast for breakfast\"\nor snap a photo of your meal.")
+                                    .font(.subheadline)
+                                    .foregroundStyle(Color.textSecondary)
+                                    .multilineTextAlignment(.center)
+                                    .lineSpacing(4)
+                                Spacer(minLength: 60)
+                            }
+                            .frame(maxWidth: .infinity)
+                            .padding(.horizontal, 32)
+                        }
+
                         ForEach(vm.messages) { message in
                             chatBubble(message)
                                 .id(message.id)