feat(macos): add native menu bar app with notch overlay

Introduces a SwiftUI companion app for the Fail Well PWA: menu bar
status item, popover with task list / record / history views, command
palette, and a Dynamic Island-style notch overlay that shows the active
step and timer beside the hardware notch and expands on hover to reveal
pause/next controls.

macos/Sources/FailWell/Services/EstimationComparator.swift

@@ -0,0 +1,13 @@
+import Foundation
+
+enum EstimationComparator {
+    /// Returns `true` when the actual duration deviates from the estimation by more than
+    /// 10 % (with a 1-minute floor for very short steps). Mirrors `is10PercentOffThanEstimation`.
+    static func is10PercentOff(estimation: Double, duration: Double) -> Bool {
+        abs(duration - estimation) > max(estimation * 0.1, 1)
+    }
+
+    static func is10PercentOff(estimation: Int, duration: Int) -> Bool {
+        is10PercentOff(estimation: Double(estimation), duration: Double(duration))
+    }
+}