sweep: name voice-daemon magic numbers, drop dead keep-alive vars (V-581)

mavsttd/whisper_handler.go: name the no_speech_prob confidence-zeroing
floor (0.9) and the whisper thread count (4), both previously bare
literals with no reason attached.

mavttsd/piper_handler.go: name piper's render rate (22050) and the
canonical wire rate (16000) used by the resampler, instead of repeating
the two numbers inline four times.

mavenclient/main.go: remove the strconv/io/net/time imports and their
`var _ = ...` keep-alive lines — dead weight with no caller, not future
scaffolding.

Behaviour-preserving; no test changed. go test -race ./internal/...
./cmd/... is green.

cmd/mavttsd/piper_handler.go

@@ -116,18 +116,27 @@ func (h *piperHandler) Synthesize(ctx context.Context, req worker.SynthesizeReq)
 	}, nil
 }
 
-// resample22050To16000 converts raw 16-bit PCM from 22050 Hz to 16000 Hz
-// using linear interpolation.
+// piperSampleRate is the rate piper's onnx voices render at (ru_RU-irina and
+// the other models this daemon has been pointed at). targetSampleRate is the
+// canonical maven wire rate (audio.PCM16kMono) that every downstream
+// consumer — playback, the voice wire, whisper on the way back in — expects.
+const (
+	piperSampleRate  = 22050
+	targetSampleRate = 16000
+)
+
+// resample22050To16000 converts raw 16-bit PCM from piperSampleRate to
+// targetSampleRate using linear interpolation.
 func resample22050To16000(input []byte) []byte {
 	if len(input) < 2 {
 		return nil
 	}
 
 	nSamples := len(input) / 2
-	outSamples := int(float64(nSamples) * 16000.0 / 22050.0)
+	outSamples := int(float64(nSamples) * float64(targetSampleRate) / float64(piperSampleRate))
 	output := make([]byte, outSamples*2)
 
-	ratio := 22050.0 / 16000.0
+	ratio := float64(piperSampleRate) / float64(targetSampleRate)
 
 	for i := 0; i < outSamples; i++ {
 		srcPos := float64(i) * ratio