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/lib/services/crypto_service.dart

@@ -2,7 +2,7 @@ import 'dart:convert';
 import 'dart:math';
 import 'dart:typed_data';
 import 'package:crypto/crypto.dart';
-import 'package:pointycastle/export.dart' as pc;
+
 
 class CryptoService {
   static const int keySize = 32;
@@ -28,20 +28,40 @@ class CryptoService {
   }
 
   Uint8List deriveKey(String password, Uint8List salt) {
-    final key = pbkdf2(
-      hash: sha256,
-      password: utf8.encode(password),
-      salt: salt,
-      iterations: 100000,
-      keyLength: keySize,
-    );
-    return Uint8List.fromList(key);
+    return _pbkdf2(sha256, utf8.encode(password), salt, 100000, keySize);
+  }
+
+  static Uint8List _pbkdf2(Hash hash, List<int> password, List<int> salt, int iterations, int keyLength) {
+    const hLen = 32;
+    final blocks = (keyLength + hLen - 1) ~/ hLen;
+    final result = Uint8List(keyLength);
+
+    for (int block = 1; block <= blocks; block++) {
+      final blockBytes = ByteData(4)..setUint32(0, block, Endian.big);
+      final blockSalt = Uint8List.fromList([...salt, ...blockBytes.buffer.asUint8List()]);
+      final prf = Hmac(hash, password);
+      var u = prf.convert(blockSalt).bytes;
+      var t = Uint8List.fromList(u);
+
+      for (int i = 1; i < iterations; i++) {
+        u = prf.convert(u).bytes;
+        for (int j = 0; j < hLen; j++) {
+          t[j] ^= u[j];
+        }
+      }
+
+      final offset = (block - 1) * hLen;
+      final length = min(hLen, keyLength - offset);
+      result.setRange(offset, offset + length, t.sublist(0, length));
+    }
+
+    return result;
   }
 
   Uint8List encrypt(Uint8List plaintext, Uint8List key) {
-    final nonce = generateNonce();
     final hmac = Hmac(sha256, key);
     final mac = hmac.convert(plaintext).bytes;
+    final nonce = generateNonce();
 
     final result = Uint8List(nonce.length + mac.length + plaintext.length);
     result.setAll(0, nonce);
@@ -54,7 +74,6 @@ class CryptoService {
   Uint8List? decrypt(Uint8List ciphertext, Uint8List key) {
     try {
       if (ciphertext.length < nonceSize + 32) return null;
-      final nonce = ciphertext.sublist(0, nonceSize);
       final mac = ciphertext.sublist(nonceSize, nonceSize + 32);
       final plaintext = ciphertext.sublist(nonceSize + 32);