feat: My Tasks widget, event countdown redesign, completed section

- My Tasks widget: today's tasks with interactive check-off (ToggleTaskIntent)
  and a "+" that opens the app's add-task sheet; writes preserve all task
  fields and sync via the App Group.
- Event Countdown: AZURE/AWS-style header (accent name + countdown label +
  percent); tap the label to cycle days → weeks → time remaining.
- Today: collapsible "Completed" archive section below Upcoming.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

KisaniCal/Views/TodayView.swift

@@ -123,6 +123,16 @@ struct TodayView: View {
                         )
                     }
 
+                    // ── Completed (all, collapsible) ──
+                    if !taskVM.completedTasks.isEmpty {
+                        CompletedSection(
+                            tasks: taskVM.completedTasks,
+                            onUndo: { taskVM.toggle($0) }
+                        )
+                        .padding(.horizontal, 18)
+                        .padding(.top, 10)
+                    }
+
                     let hasAnything = !taskVM.overdueTasks.isEmpty || !taskVM.todayTasks.isEmpty
                         || !taskVM.upcomingTasks.isEmpty || !taskVM.completedTodayTasks.isEmpty
                         || !taskVM.next3DaysTasks.isEmpty || !todayCalEvents.isEmpty
@@ -1009,6 +1019,74 @@ struct CompletedTodaySection: View {
     }
 }
 
+// MARK: - Completed Section (all completed, collapsible archive)
+struct CompletedSection: View {
+    @Environment(\.colorScheme) private var cs
+    let tasks: [TaskItem]
+    let onUndo: (TaskItem) -> Void
+
+    @State private var expanded = false
+
+    private let dateFmt: DateFormatter = {
+        let f = DateFormatter(); f.dateFormat = "MMM d"; return f
+    }()
+
+    var body: some View {
+        VStack(spacing: 0) {
+            // Header
+            HStack {
+                Text("Completed")
+                    .font(AppFonts.sans(15, weight: .bold))
+                    .foregroundColor(AppColors.text2(cs))
+                Spacer()
+                Text("\(tasks.count)")
+                    .font(AppFonts.mono(11))
+                    .foregroundColor(AppColors.text3(cs))
+                Image(systemName: "chevron.down")
+                    .font(.system(size: 11, weight: .semibold))
+                    .foregroundColor(AppColors.text3(cs))
+                    .rotationEffect(.degrees(expanded ? 0 : -90))
+                    .animation(KisaniSpring.micro, value: expanded)
+            }
+            .padding(.horizontal, 14).padding(.vertical, 12)
+            .contentShape(Rectangle())
+            .onTapGesture { withAnimation(KisaniSpring.snappy) { expanded.toggle() } }
+
+            if expanded {
+                ForEach(tasks) { task in
+                    HStack(spacing: 12) {
+                        Button {
+                            withAnimation(KisaniSpring.snappy) { onUndo(task) }
+                        } label: {
+                            Image(systemName: "checkmark.square.fill")
+                                .font(.system(size: 22))
+                                .foregroundColor(AppColors.text3(cs).opacity(0.6))
+                        }
+                        .buttonStyle(.plain)
+
+                        Text(task.title)
+                            .font(AppFonts.sans(14))
+                            .foregroundColor(AppColors.text3(cs))
+                            .strikethrough(true, color: AppColors.text3(cs).opacity(0.7))
+                            .lineLimit(1)
+                        Spacer(minLength: 8)
+                        if let d = task.completedAt {
+                            Text(dateFmt.string(from: d))
+                                .font(AppFonts.sans(13))
+                                .foregroundColor(AppColors.text3(cs))
+                        }
+                    }
+                    .padding(.horizontal, 14).padding(.vertical, 10)
+                }
+                .padding(.bottom, 4)
+            }
+        }
+        .background(AppColors.surface(cs))
+        .clipShape(RoundedRectangle(cornerRadius: AppRadius.large))
+        .overlay(RoundedRectangle(cornerRadius: AppRadius.large).stroke(AppColors.border(cs), lineWidth: 1))
+    }
+}
+
 // MARK: - Task Row
 struct TaskRowView: View {
     @Environment(\.colorScheme) private var cs