fix: skip silent recordings instead of transcribing them

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Sources/SstCore/DictationController.swift

@@ -13,20 +13,24 @@ public final class DictationController {
     private let cleaner: Cleaner
     private let inserter: TextInserting
     private let minimumSamples: Int
+    private let silenceThreshold: Float
 
     /// - Parameter minimumSamples: 16 kHz samples; default is 0.3 s.
+    /// - Parameter silenceThreshold: RMS below which a recording counts as silence and is skipped.
     public init(
         recorder: AudioRecording,
         transcriber: Transcriber,
         cleaner: Cleaner,
         inserter: TextInserting,
-        minimumSamples: Int = 4_800
+        minimumSamples: Int = 4_800,
+        silenceThreshold: Float = 0.005
     ) {
         self.recorder = recorder
         self.transcriber = transcriber
         self.cleaner = cleaner
         self.inserter = inserter
         self.minimumSamples = minimumSamples
+        self.silenceThreshold = silenceThreshold
     }
 
     public func handle(_ event: HotkeyEvent) async {
@@ -44,6 +48,11 @@ public final class DictationController {
                 state = .idle
                 return
             }
+            let energy = samples.reduce(0) { $0 + $1 * $1 }
+            guard (energy / Float(samples.count)).squareRoot() >= silenceThreshold else {
+                state = .idle
+                return
+            }
             await process(samples)
         default:
             break