Stage 5: History, the shared daily Streak and Reminders

- Streak computed from all complete Sessions: Grace Hour (00:00-01:00
  counts for yesterday unless it is done), a Freeze per 7 Streak Days
  (max 2) spent automatically on a missed day (ADR 0006)
- Top bar flame (grey until today is done) opening a panel with current
  and longest Streak, Freezes and a month calendar; 'Day N of your
  streak' on a fresh summary
- History per Mode grouped by day, reopening each summary
- Two adjustable Reminders (19:00, 22:30) scheduled 14 days ahead with
  flutter_local_notifications, none on a done day; permission asked
  after the first complete Session or from Settings
- Settings: Reminders, the Player chime, exercise credits

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -11,6 +11,8 @@ android {
     ndkVersion = "27.0.12077973"
 
     compileOptions {
+        // Desugaring: flutter_local_notifications needs java.time on older Android versions.
+        isCoreLibraryDesugaringEnabled = true
         sourceCompatibility = JavaVersion.VERSION_11
         targetCompatibility = JavaVersion.VERSION_11
     }
@@ -42,3 +44,7 @@ android {
 flutter {
     source = "../.."
 }
+
+dependencies {
+    coreLibraryDesugaring("com.android.tools:desugar_jdk_libs:2.1.4")
+}