build(meezi_app): Flutter Koja now builds for web (mirror + platform gen + fixes)

Connectivity fixed: pub.dev/googleapis are 403 under sanctions, so PUB_HOSTED_URL
+ FLUTTER_STORAGE_BASE_URL now point at the reachable Flutter mirror
(pub.flutter-io.cn / storage.flutter-io.cn) — set persistently on the build machine.

- `flutter create --platforms=android,web --org ir.meezi` generated android/ + web/
  (#33). `flutter build web` succeeds; `flutter analyze` errors all cleared.
- pubspec: intl ^0.19.0 → ^0.20.2 (SDK pins 0.20.2 via flutter_localizations).
- Fixed 3 pre-existing compile errors (app had never been built):
  * attendance: JalaliFormatter.yyyyMMdd() removed → build the date from year/month/day.
  * qr_scan: dropped a call to a non-existent CartNotifier.setTable (table context is
    already set via tableContextProvider just above).
  * widget_test: default counter test referenced MyApp → minimal MeeziApp smoke test.
- discover_screen: drop redundant foundation import; value → initialValue (non-deprecated).

Verified: flutter build web ✓. (Android packaging still needs a Gradle/Maven mirror.)

mobile/meezi_app/lib/features/discover/discover_screen.dart

@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import 'package:flutter/foundation.dart' show ValueGetter;
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
@@ -210,7 +209,7 @@ class _DiscoverScreenState extends ConsumerState<DiscoverScreen> {
             Padding(
               padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
               child: DropdownButtonFormField<String>(
-                value: filters.sort,
+                initialValue: filters.sort,
                 decoration: const InputDecoration(
                   labelText: 'مرتب‌سازی',
                   isDense: true,