feat(sdk): 帧间隔 frameIntervalMs 配置化（默认 35ms，[0,500] clamp）

DuooomiBleConfig 新增 frameIntervalMs，BleProtocolService 构造期注入。
顺手清死代码 FrameConstants.frameIntervalNanos、修 sendFrames 0.035 字面量
（统一走 config）。demo 加可调输入框 + UserDefaults 持久化。
越界 warn 不抛错，使用点 min/max 兜底。

设计稿：docs/superpowers/specs/2026-05-20-frame-interval-config-design.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

demo/Sources/DemoApp.swift

@@ -29,6 +29,9 @@ final class DemoViewModel: NSObject, ObservableObject, DuooomiBleSDKDelegate {
     @Published var configScanPrefix: String {
         didSet { defaults.set(configScanPrefix, forKey: Self.keyScanPrefix) }
     }
+    @Published var configFrameIntervalMs: String {
+        didSet { defaults.set(configFrameIntervalMs, forKey: Self.keyFrameIntervalMs) }
+    }
 
     // MARK: - SDK State (driven by delegate)
 
@@ -50,26 +53,31 @@ final class DemoViewModel: NSObject, ObservableObject, DuooomiBleSDKDelegate {
     private static let keyBrand = "demo.config.brand"
     private static let keyApiKey = "demo.config.apiKey"
     private static let keyScanPrefix = "demo.config.scanPrefix"
+    private static let keyFrameIntervalMs = "demo.config.frameIntervalMs"
 
     /// demo 调试默认值（仅当 UserDefaults 没存过时使用）。秘钥从 DemoSecrets 读，避免泄露到仓库。
     private static let defaultBrand = DemoSecrets.brand
     private static let defaultApiKey = DemoSecrets.apiKey
     private static let defaultScanPrefix = DemoSecrets.scanNamePrefix
+    private static let defaultFrameIntervalMs = "35"
 
     override init() {
         let d = UserDefaults.standard
         let brand = d.string(forKey: Self.keyBrand) ?? Self.defaultBrand
         let apiKey = d.string(forKey: Self.keyApiKey) ?? Self.defaultApiKey
         let scanPrefix = d.string(forKey: Self.keyScanPrefix) ?? Self.defaultScanPrefix
+        let frameIntervalMs = d.string(forKey: Self.keyFrameIntervalMs) ?? Self.defaultFrameIntervalMs
 
         self.configBrand = brand
         self.configApiKey = apiKey
         self.configScanPrefix = scanPrefix
+        self.configFrameIntervalMs = frameIntervalMs
 
         self.sdk = DuooomiBleSDK(config: .init(
             apiKey: apiKey,
             brand: brand,
-            scanNamePrefix: scanPrefix
+            scanNamePrefix: scanPrefix,
+            frameIntervalMs: Int(frameIntervalMs) ?? 35
         ))
 
         super.init()
@@ -83,7 +91,8 @@ final class DemoViewModel: NSObject, ObservableObject, DuooomiBleSDKDelegate {
         let new = DuooomiBleSDK(config: .init(
             apiKey: configApiKey,
             brand: configBrand,
-            scanNamePrefix: configScanPrefix
+            scanNamePrefix: configScanPrefix,
+            frameIntervalMs: Int(configFrameIntervalMs) ?? 35
         ))
         new.delegate = self
         self.sdk = new