feat: 支持手动切换采集帧率

在 Android、Web 及 Flutter 控制端新增帧率选择 UI，被控端按屏幕刷新率生成支持的帧率档位并上报，允许在保持分辨率不变的情况下仅切换帧率。

另附带更新信号服务器的数据库配置。

webrtc_controller_flutter/lib/proto/control_message.pb.dart

@@ -40,6 +40,7 @@ class ControlMessage extends $pb.GeneratedMessage {
     $core.int? height,
     $core.int? fps,
     $core.int? streamMode,
+    $core.Iterable<$core.int>? supportedFps,
   }) {
     final result = create();
     if (action != null) result.action = action;
@@ -57,6 +58,7 @@ class ControlMessage extends $pb.GeneratedMessage {
     if (height != null) result.height = height;
     if (fps != null) result.fps = fps;
     if (streamMode != null) result.streamMode = streamMode;
+    if (supportedFps != null) result.supportedFps.addAll(supportedFps);
     return result;
   }
 
@@ -89,6 +91,7 @@ class ControlMessage extends $pb.GeneratedMessage {
     ..aI(13, _omitFieldNames ? '' : 'height')
     ..aI(14, _omitFieldNames ? '' : 'fps')
     ..aI(15, _omitFieldNames ? '' : 'stream_mode')
+    ..p<$core.int>(16, _omitFieldNames ? '' : 'supportedFps', $pb.PbFieldType.K3)
     ..hasRequiredFields = false;
 
   @$core.Deprecated('See https://github.com/google/protobuf.dart/issues/998.')
@@ -254,6 +257,10 @@ class ControlMessage extends $pb.GeneratedMessage {
   $core.bool hasStreamMode() => $_has(14);
   @$pb.TagNumber(15)
   void clearStreamMode() => $_clearField(15);
+
+  /// 被控端支持的帧率档位列表（REPORT_RESOLUTION 上报，按屏幕刷新率筛选，升序）。
+  @$pb.TagNumber(16)
+  $pb.PbList<$core.int> get supportedFps => $_getList(15);
 }
 
 const $core.bool _omitFieldNames =