сборка: APK (Android) + Linux Desktop

- Исправлены ошибки Flutter анализа (withOpacity, pbkdf2, импорты)
- Упрощён pubspec.yaml (только нужные зависимости)
- Android APK собран: build/app/outputs/flutter-apk/app-release.apk (22MB)
- Linux Desktop собран: build/linux/x64/release/bundle/jam_client

Для Windows: кросс-компиляция невозможна с Linux.
Нужен Windows хост для flutter build windows.

client/web/manifest.json

@@ -1,21 +1,35 @@
 {
-  "name": "JustAMessenger",
-  "short_name": "JAM",
-  "start_url": ".",
-  "display": "standalone",
-  "background_color": "#313338",
-  "theme_color": "#5865F2",
-  "description": "Lightweight Decentralized Messenger",
-  "icons": [
-    {
-      "src": "icons/Icon-192.png",
-      "sizes": "192x192",
-      "type": "image/png"
-    },
-    {
-      "src": "icons/Icon-512.png",
-      "sizes": "512x512",
-      "type": "image/png"
-    }
-  ]
+    "name": "jam_client",
+    "short_name": "jam_client",
+    "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"
+        }
+    ]
 }