Add daily streak system and normalize bundle id to com.airkjw.blockseasons

Pure advanceStreak (1-day grace none, milestone flags at 3/7/14/30),
persisted in the save blob; StreakNotifier advances on every finished
attempt; home screen flame chip and milestone snackbar. Fix flutter
create's camelCased iOS bundle id and underscored Android application
id to the agreed lowercase form before any store registration.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/data/streak.dart

@@ -0,0 +1,49 @@
+/// Daily streak: at least one stage attempt (win or lose) per local
+/// calendar day keeps it alive. No clock-cheat defense — single-player,
+/// low stakes.
+class StreakState {
+  const StreakState({
+    required this.current,
+    required this.best,
+    required this.lastYmd,
+    this.hitMilestone,
+  });
+
+  static const initial = StreakState(current: 0, best: 0, lastYmd: null);
+
+  static const milestones = [3, 7, 14, 30];
+
+  final int current;
+  final int best;
+
+  /// Local date of the last counted play, as `yyyy-MM-dd`.
+  final String? lastYmd;
+
+  /// Set when this advance just reached a milestone (celebrate once).
+  final int? hitMilestone;
+}
+
+String _ymd(DateTime d) =>
+    '${d.year.toString().padLeft(4, '0')}-'
+    '${d.month.toString().padLeft(2, '0')}-'
+    '${d.day.toString().padLeft(2, '0')}';
+
+StreakState advanceStreak(StreakState state, DateTime now) {
+  final today = _ymd(now);
+  if (state.lastYmd == today) {
+    return StreakState(
+      current: state.current,
+      best: state.best,
+      lastYmd: today,
+    );
+  }
+  // Normalized constructor handles month/year boundaries (and DST).
+  final yesterday = _ymd(DateTime(now.year, now.month, now.day - 1));
+  final current = state.lastYmd == yesterday ? state.current + 1 : 1;
+  return StreakState(
+    current: current,
+    best: current > state.best ? current : state.best,
+    lastYmd: today,
+    hitMilestone: StreakState.milestones.contains(current) ? current : null,
+  );
+}