feat(monetization-261): prepare entitlement infrastructure and quota enforcement for release

- Add EntitlementSnapshot, EntitlementRevalidationUseCase, and BillingUseCases
- Add DriftEntitlementSnapshotRepository for offline entitlement caching
- Add HealthConnect gateway and integration
- Add quota enforcement in share acceptance (server and UI)
- Add entitlement API endpoints in server
- Add privacy policy v1 and release compliance checklist
- Add QA gates and device runbooks for release validation
- Add demo content screen and settings screen

Ticket #261

lib/infrastructure/local/app_database.dart

@@ -52,7 +52,7 @@ final class AppDatabase extends _$AppDatabase {
   }
 
   @override
-  int get schemaVersion => 26;
+  int get schemaVersion => 27;
 
   @override
   MigrationStrategy get migration {
@@ -62,6 +62,7 @@ final class AppDatabase extends _$AppDatabase {
         await _migrateToSchema15();
         await _migrateToSchema16(migrator);
         await _migrateToSchema25();
+        await _migrateToSchema27();
         await _createIndexes();
       },
       onUpgrade: (migrator, from, to) async {
@@ -145,6 +146,9 @@ final class AppDatabase extends _$AppDatabase {
         if (from < 26) {
           await _migrateToSchema26(migrator);
         }
+        if (from < 27) {
+          await _migrateToSchema27();
+        }
         await _createIndexes();
       },
       beforeOpen: (details) async {
@@ -485,6 +489,23 @@ extension on AppDatabase {
     await migrator.createTable(activeWorkoutTelemetryWindowStates);
   }
 
+  Future<void> _migrateToSchema27() async {
+    await customStatement('''
+CREATE TABLE IF NOT EXISTS entitlement_snapshots (
+  id TEXT NOT NULL PRIMARY KEY CHECK (id = 'current'),
+  entitlement TEXT NOT NULL CHECK (entitlement IN ('free', 'pro')),
+  can_sync INTEGER NOT NULL CHECK (can_sync IN (0, 1)),
+  has_unlimited_editable_library INTEGER NOT NULL CHECK (
+    has_unlimited_editable_library IN (0, 1)
+  ),
+  remaining_editable_slots INTEGER CHECK (
+    remaining_editable_slots IS NULL OR remaining_editable_slots >= 0
+  ),
+  validated_at INTEGER NOT NULL
+)
+''');
+  }
+
   Future<void> _migrateToSchema13() async {
     await customStatement('PRAGMA foreign_keys = OFF');
     await customStatement('''