feat: add remote products and qr code for payconic

lib/database/app_database.dart

@@ -36,8 +36,13 @@ class Products extends Table {
 
   IntColumn get priceInCents => integer()();
 
+  /// The picture shown on the tile: a local file, also offline.
   TextColumn get imagePath => text().nullable()();
 
+  /// The server's picture of this product (`/images/<imageId>`); [imagePath]
+  /// is its downloaded copy once that finished. Null: none on the server.
+  TextColumn get imageId => text().nullable()();
+
   BoolColumn get active => boolean().withDefault(const Constant(true))();
 
   @override
@@ -227,6 +232,22 @@ class StockAdjustmentResults extends Table {
   Set<Column> get primaryKey => {id};
 }
 
+/// Pictures taken on this tablet, waiting to be uploaded. Once uploaded, the
+/// product points at the server's copy and the row is removed; offline it
+/// waits here, while the tile already shows the local file.
+@DataClassName('PendingImageUploadRow')
+class PendingImageUploads extends Table {
+  /// One picture per product: a newer one replaces a waiting one.
+  TextColumn get productId => text()();
+
+  TextColumn get localPath => text()();
+
+  DateTimeColumn get createdAt => dateTime()();
+
+  @override
+  Set<Column> get primaryKey => {productId};
+}
+
 @DriftDatabase(
   tables: [
     Products,
@@ -240,13 +261,14 @@ class StockAdjustmentResults extends Table {
     ProcessedRemoteCommands,
     TabEvents,
     StockAdjustmentResults,
+    PendingImageUploads,
   ],
 )
 class AppDatabase extends _$AppDatabase {
   AppDatabase([QueryExecutor? executor]) : super(executor ?? _openConnection());
 
   @override
-  int get schemaVersion => 17;
+  int get schemaVersion => 18;
 
   @override
   MigrationStrategy get migration {
@@ -362,6 +384,13 @@ class AppDatabase extends _$AppDatabase {
             remoteSyncState.settlementsCursor,
           );
         }
+
+        if (from < 18) {
+          if (!await hasTableColumn('products', 'image_id')) {
+            await migrator.addColumn(products, products.imageId);
+          }
+          await migrator.createTable(pendingImageUploads);
+        }
       },
     );
   }