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/web/manifest.json

@@ -0,0 +1,35 @@
+{
+    "name": "meezi_app",
+    "short_name": "meezi_app",
+    "start_url": ".",
+    "display": "standalone",
+    "background_color": "#0175C2",
+    "theme_color": "#0175C2",
+    "description": "A new Flutter project.",
+    "orientation": "portrait-primary",
+    "prefer_related_applications": false,
+    "icons": [
+        {
+            "src": "icons/Icon-192.png",
+            "sizes": "192x192",
+            "type": "image/png"
+        },
+        {
+            "src": "icons/Icon-512.png",
+            "sizes": "512x512",
+            "type": "image/png"
+        },
+        {
+            "src": "icons/Icon-maskable-192.png",
+            "sizes": "192x192",
+            "type": "image/png",
+            "purpose": "maskable"
+        },
+        {
+            "src": "icons/Icon-maskable-512.png",
+            "sizes": "512x512",
+            "type": "image/png",
+            "purpose": "maskable"
+        }
+    ]
+}