Clear demo data, namespace storage by user, add profile setup

- Remove all personal sampleTasks from TaskViewModel (tasks start empty)
- Namespace UserDefaults keys by Apple ID for task and workout data isolation
- Add ProfileSetupView for name capture after first Sign in with Apple
- Add updateDisplayName() to AuthManager
- Route to ProfileSetupView when user has no display name yet

Co-Authored-By: Kutesir <tqwyy79vzn@privaterelay.appleid.com>

KisaniCal/Views/ProfileSetupView.swift

@@ -0,0 +1,85 @@
+import SwiftUI
+
+struct ProfileSetupView: View {
+    @ObservedObject private var auth = AuthManager.shared
+    @Environment(\.colorScheme) private var cs
+    @State private var name = ""
+    @FocusState private var focused: Bool
+
+    var body: some View {
+        ZStack {
+            AppColors.background(cs).ignoresSafeArea()
+
+            VStack(spacing: 0) {
+                Spacer()
+
+                VStack(spacing: 24) {
+                    ZStack {
+                        RoundedRectangle(cornerRadius: 24)
+                            .fill(AppColors.accentSoft)
+                            .frame(width: 88, height: 88)
+                        Image(systemName: "person.fill")
+                            .font(.system(size: 36, weight: .light))
+                            .foregroundColor(AppColors.accent)
+                    }
+
+                    VStack(spacing: 8) {
+                        Text("What's your name?")
+                            .font(AppFonts.sans(26, weight: .bold))
+                            .foregroundColor(AppColors.text(cs))
+                        Text("This is how you'll appear in the app.")
+                            .font(AppFonts.sans(15))
+                            .foregroundColor(AppColors.text2(cs))
+                            .multilineTextAlignment(.center)
+                    }
+                }
+
+                Spacer()
+
+                VStack(spacing: 16) {
+                    TextField("Your name", text: $name)
+                        .font(AppFonts.sans(17))
+                        .foregroundColor(AppColors.text(cs))
+                        .padding(.horizontal, 18)
+                        .padding(.vertical, 16)
+                        .background(
+                            RoundedRectangle(cornerRadius: 14)
+                                .fill(Color(uiColor: cs == .dark ? .secondarySystemBackground : .systemGray6))
+                        )
+                        .padding(.horizontal, 28)
+                        .focused($focused)
+                        .submitLabel(.done)
+                        .onSubmit { save() }
+
+                    Button(action: save) {
+                        Text("Continue")
+                            .font(AppFonts.sans(17, weight: .semibold))
+                            .foregroundColor(.white)
+                            .frame(maxWidth: .infinity)
+                            .frame(height: 54)
+                            .background(
+                                RoundedRectangle(cornerRadius: 14)
+                                    .fill(name.trimmingCharacters(in: .whitespaces).isEmpty
+                                          ? AppColors.accent.opacity(0.4)
+                                          : AppColors.accent)
+                            )
+                    }
+                    .disabled(name.trimmingCharacters(in: .whitespaces).isEmpty)
+                    .padding(.horizontal, 28)
+
+                    Button("Skip for now") {
+                        auth.updateDisplayName("User")
+                    }
+                    .font(AppFonts.sans(14))
+                    .foregroundColor(AppColors.text3(cs))
+                }
+                .padding(.bottom, 56)
+            }
+        }
+        .onAppear { focused = true }
+    }
+
+    private func save() {
+        auth.updateDisplayName(name)
+    }
+}