feat: start at Season 1, add menu/season_001 BGM tracks, settings build tag

- activeSeason now returns the first season (Season 1 'First Bloom') so a new
  player starts at spring instead of the newest season.
- Bundle the owner-picked CC0 tracks menu.mp3 + season_001.mp3 (BGM now audible).
- Settings footer shows 'v1.0.0 (build 3)' so test builds are identifiable.
180 tests green, analyze clean.

lib/state/providers.dart

@@ -76,9 +76,12 @@ final seasonRefreshProvider = FutureProvider<bool>(
   (ref) => ref.read(contentRepositoryProvider).refresh(),
 );
 
-/// The season players land in by default: the newest available.
-/// (availableSeasons is sorted by seasonId ascending.)
-SeasonPack activeSeason(List<SeasonPack> seasons) => seasons.last;
+/// The season players land in by default: Season 1, the start of the journey,
+/// so a new player experiences the content in order rather than being dropped
+/// into the newest season. (availableSeasons is sorted by seasonId ascending,
+/// so `.first` is Season 1.) A season selector to reach later seasons is a
+/// planned follow-up.
+SeasonPack activeSeason(List<SeasonPack> seasons) => seasons.first;
 
 final streakProvider = NotifierProvider<StreakNotifier, StreakState>(
   StreakNotifier.new,

lib/ui/screens/settings_screen.dart

@@ -76,6 +76,16 @@ class SettingsScreen extends ConsumerWidget {
                 title: Text(l10n.restorePurchases),
                 onTap: () => iap.restorePurchases(),
               ),
+              const SizedBox(height: 24),
+              Center(
+                child: Text(
+                  'Block Seasons · v1.0.0 (build 3)',
+                  style: TextStyle(
+                    color: Colors.white.withValues(alpha: 0.4),
+                    fontSize: 12,
+                  ),
+                ),
+              ),
             ],
           ),
         ),

test/state/season_refresh_test.dart

@@ -51,9 +51,9 @@ void main() {
     expect(repo.calls, 1);
   });
 
-  test('activeSeason picks the newest by id', () {
+  test('activeSeason starts at Season 1 (first by id)', () {
     final p1 = _pack('season_001');
     final p2 = _pack('season_002');
-    expect(activeSeason([p1, p2]).seasonId, 'season_002');
+    expect(activeSeason([p1, p2]).seasonId, 'season_001');
   });
 }