feat: 统计按键触发到正在录音的延迟并在日志中打印

每次长按进入 Recording 状态时打印本次延迟，并维护累计统计:
  ⏱ 按键→录音延迟: 123ms (平均: 120ms, 最小: 98ms, 最大: 155ms, 累计: 5次)

使用 QElapsedTimer 精确计时。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/core/voice_input_service.cpp

@@ -19,6 +19,8 @@
 #include <QThread>
 #include <QTimer>
 #include <QtConcurrent>
+#include <QElapsedTimer>
+#include <algorithm>
 
 static const char* const kTag = "VoiceInputService";
 
@@ -48,6 +50,22 @@ VoiceInputService::VoiceInputService(ConfigManager* configManager,
             state_ = Recording;
             audioBuffer_.clear(); // 清除预录音期间的静音
             emit statusChanged("正在录音...");
+
+            // 统计按键到录音延迟
+            if (latencyTracking_ && hotkeyLatencyTimer_.isValid()) {
+                qint64 latencyMs = hotkeyLatencyTimer_.elapsed();
+                totalKeyCount_++;
+                totalLatencyMs_ += latencyMs;
+                maxLatencyMs_ = std::max(maxLatencyMs_, (double)latencyMs);
+                minLatencyMs_ = std::min(minLatencyMs_, (double)latencyMs);
+                double avgMs = totalLatencyMs_ / totalKeyCount_;
+                LOG_INFO(kTag, QString("⏱ 按键→录音延迟: %1ms (平均: %2ms, 最小: %3ms, 最大: %4ms, 累计: %5次)")
+                    .arg(latencyMs).arg(avgMs, 0, 'f', 0)
+                    .arg(minLatencyMs_, 0, 'f', 0).arg(maxLatencyMs_, 0, 'f', 0)
+                    .arg(totalKeyCount_));
+                latencyTracking_ = false;
+            }
+
             LOG_DEBUG(kTag, "PreRecording → Recording (灯保持 ON，开始录音)");
         }
     });
@@ -156,6 +174,10 @@ void VoiceInputService::onHotkeyActivated() {
     recording_ = true;
     audioBuffer_.clear();
 
+    // 启动延迟统计
+    hotkeyLatencyTimer_.start();
+    latencyTracking_ = true;
+
     int deviceIndex = configManager_->get("audio.input_device").toInt();
     int sampleRate = configManager_->get("stt.sample_rate").toInt();
     int bufferSizeMs = configManager_->get("audio.buffer_size_ms").toInt();

src/core/voice_input_service.h

@@ -3,6 +3,7 @@
 #include <QObject>
 #include <QString>
 #include <QTimer>
+#include <QElapsedTimer>
 #include <vector>
 #include <memory>
 
@@ -80,6 +81,15 @@ private:
     QTimer* longPressTimer_ = nullptr;
     QTimer* cooldownTimer_ = nullptr;
 
+    // 按键到录音延迟统计
+    QElapsedTimer hotkeyLatencyTimer_;
+    bool latencyTracking_ = false;
+
+    int totalKeyCount_ = 0;
+    double totalLatencyMs_ = 0;
+    double maxLatencyMs_ = 0;
+    double minLatencyMs_ = 9999;
+
     void startRecording();
     void stopRecordingAndTranscribe();
     void simulateCapsLock();