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_ios/web_rtc_controller_ios/ViewModel/ControllerViewModel.swift

@@ -56,6 +56,10 @@ final class ControllerViewModel: NSObject, ObservableObject {
     @Published var statsText: String = ""
     @Published var streamMode: StreamMode = .webrtc
     @Published var selectedResolution: ResolutionOption = ResolutionOption.all[0]
+    /// 帧率档位：默认常用档位，收到被控端上报的 supported_fps 后以上报列表为准
+    @Published var fpsOptions: [Int] = [15, 24, 30, 60]
+    /// 被控端当前采集帧率（0 表示尚未收到上报）
+    @Published var currentFps: Int = 0
     /// 远端视频宽高比（宽/高），用于让触控层与画面精确对齐
     @Published var videoAspect: CGFloat = 9.0 / 16.0
     @Published var showAuthSheet: Bool = false
@@ -82,6 +86,9 @@ final class ControllerViewModel: NSObject, ObservableObject {
     private var pendingAuthValue: String = ""
     /// 是否为本端主动切换串流模式（避免上报回环再次发送）
     private var suppressStreamModeSend = false
+    /// 被控端最近上报的实际采集尺寸（仅切帧率时保持分辨率不变，0 表示原生）
+    private var lastReportedWidth: Int32 = 0
+    private var lastReportedHeight: Int32 = 0
 
     override init() {
         super.init()
@@ -138,6 +145,10 @@ final class ControllerViewModel: NSObject, ObservableObject {
         statsText = ""
         streamMode = .webrtc
         selectedResolution = ResolutionOption.all[0]
+        fpsOptions = [15, 24, 30, 60]
+        currentFps = 0
+        lastReportedWidth = 0
+        lastReportedHeight = 0
         videoAspect = 9.0 / 16.0
     }
 
@@ -192,6 +203,14 @@ final class ControllerViewModel: NSObject, ObservableObject {
         webRTCClient?.requestResolutionChange(width: option.width, height: option.height, fps: 0)
     }
 
+    /// 仅切换帧率：分辨率沿用被控端最近上报的实际采集尺寸（0 表示原生）
+    func selectFps(_ fps: Int) {
+        guard fps > 0, fps != currentFps else { return }
+        webRTCClient?.requestResolutionChange(width: lastReportedWidth,
+                                              height: lastReportedHeight,
+                                              fps: Int32(fps))
+    }
+
     func toggleStreamMode(_ selfCodecOn: Bool) {
         let newMode: StreamMode = selfCodecOn ? .selfCodec : .webrtc
         guard newMode != streamMode else { return }
@@ -441,10 +460,17 @@ extension ControllerViewModel: WebRTCClientDelegate {
 
     func webRTCClient(didReportResolution width: Int, height: Int) {
         guard width > 0, height > 0 else { return }
+        lastReportedWidth = Int32(width)
+        lastReportedHeight = Int32(height)
         if streamMode == .webrtc {
             videoAspect = CGFloat(width) / CGFloat(height)
         }
     }
+
+    func webRTCClient(didReportFps fps: Int, supportedFps: [Int]) {
+        if fps > 0 { currentFps = fps }
+        if !supportedFps.isEmpty { fpsOptions = supportedFps }
+    }
 }
 
 // MARK: - RTCVideoViewDelegate（WebRTC 模式下画面尺寸变化）