feat: поддержка медиа-вложений — опросы, видео, файлы и просмотр фото

Опросы (новый тип сообщения):
- модель Poll/PollAnswer и PollAttachment (_type: POLL)
- PollsModule: загрузка через opcode 306 (GET_POLL_UPDATES) с кэшем
- рендер опроса в баблах (вопрос, варианты, прогресс-бары, голоса)

Видео:
- getVideoUrl через opcode 83 (VIDEO_PLAY): выбор MP4_*/HLS из ответа
- полноэкранный плеер (video_player) с play/pause и перемоткой
- тап по видео в чате запускает воспроизведение

Файлы:
- getFileUrl через opcode 88 (FILE_DOWNLOAD) с корректным форматом
  {messageId, chatId, fileId} → url (раньше слался неверный {url, token})
- скачивание во временную папку и открытие системным приложением
  (path_provider, open_filex)

Фото:
- полноэкранный просмотрщик с зумом (был TODO-заглушкой)
- фикс «сжатости»: декодирование с учётом devicePixelRatio вместо ×2

pubspec.lock

@@ -137,6 +137,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "3.0.7"
+  csslib:
+    dependency: transitive
+    description:
+      name: csslib
+      sha256: "09bad715f418841f976c77db72d5398dc1253c21fb9c0c7f0b0b985860b2d58e"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.0.2"
   dart_lz4:
     dependency: "direct main"
     description:
@@ -397,6 +405,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.0.2"
+  html:
+    dependency: transitive
+    description:
+      name: html
+      sha256: "6d1264f2dffa1b1101c25a91dff0dc2daee4c18e87cd8538729773c073dbf602"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.15.6"
   http:
     dependency: transitive
     description:
@@ -613,6 +629,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.1.0"
+  open_filex:
+    dependency: "direct main"
+    description:
+      name: open_filex
+      sha256: "9976da61b6a72302cf3b1efbce259200cd40232643a467aac7370addf94d6900"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.7.0"
   package_info_plus:
     dependency: "direct main"
     description:
@@ -638,7 +662,7 @@ packages:
     source: hosted
     version: "1.9.1"
   path_provider:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: path_provider
       sha256: "50c5dd5b6e1aaf6fb3a78b33f6aa3afca52bf903a8a5298f53101fdaee55bbcd"
@@ -970,6 +994,46 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.2.0"
+  video_player:
+    dependency: "direct main"
+    description:
+      name: video_player
+      sha256: "48a7bdaa38a3d50ec10c78627abdbfad863fdf6f0d6e08c7c3c040cfd80ae36f"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.11.1"
+  video_player_android:
+    dependency: transitive
+    description:
+      name: video_player_android
+      sha256: "5d18d04084cc0cfc7afde39d0a308d4041e8ae6e9d5255bc086c263998dd1201"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.9.6"
+  video_player_avfoundation:
+    dependency: transitive
+    description:
+      name: video_player_avfoundation
+      sha256: "9338f3ec22774f88146b22f13273a446719b1da010fd200c4d1d97802156ac58"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.9.7"
+  video_player_platform_interface:
+    dependency: transitive
+    description:
+      name: video_player_platform_interface
+      sha256: "16eaed5268c571c31840dc58ef8da5f0cd4db2a98490c3b8f1cf70122546c6e0"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.7.0"
+  video_player_web:
+    dependency: transitive
+    description:
+      name: video_player_web
+      sha256: "9f3c00be2ef9b76a95d94ac5119fb843dca6f2c69e6c9968f6f2b6c9e7afbdeb"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.4.0"
   vm_service:
     dependency: transitive
     description:
@@ -1027,5 +1091,5 @@ packages:
     source: hosted
     version: "3.1.3"
 sdks:
-  dart: ">=3.10.4 <4.0.0"
-  flutter: ">=3.38.4"
+  dart: ">=3.12.0 <4.0.0"
+  flutter: ">=3.44.0"