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/Tests/FailWellTests/EstimationComparatorTests.swift

@@ -0,0 +1,13 @@
+import Testing
+@testable import FailWell
+
+@Suite("EstimationComparator")
+struct EstimationComparatorTests {
+    @Test func flagsDurationsMoreThan10PercentOff() {
+        // From `compare-with-estimation.test.ts`.
+        #expect(EstimationComparator.is10PercentOff(estimation: 10, duration: 9) == false)
+        #expect(EstimationComparator.is10PercentOff(estimation: 5, duration: 4) == false)
+        #expect(EstimationComparator.is10PercentOff(estimation: 10, duration: 5) == true)
+        #expect(EstimationComparator.is10PercentOff(estimation: 10, duration: 8) == true)
+    }
+}