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/mavsttd/whisper_handler.go

@@ -22,6 +22,18 @@ import (
 // to it before sending, so it's also the rate the silence gate assumes.
 const whisperSampleRate = 16000
 
+// whisperThreads — greedy decode is single-pass and this is a laptop CPU
+// (homesrv), not a server box; 4 was picked to leave headroom for the rest
+// of the daemons sharing the machine, not measured against a latency target.
+const whisperThreads = 4
+
+// noSpeechFloor — whisper's own no_speech_prob past this point means the
+// segment it transcribed is not speech (the model still emits token
+// probabilities for silence/noise, so a high avgLogProb-derived confidence
+// can coexist with a segment that should be zero). Read as "at least 90%
+// sure this was not speech."
+const noSpeechFloor = 0.9
+
 type whisperHandler struct {
 	ctx    *C.struct_whisper_context
 	minMs  int     // clips shorter than this are dropped (hallucination bait)
@@ -101,7 +113,7 @@ func (h *whisperHandler) Transcribe(ctx context.Context, req worker.TranscribeRe
 	params.print_realtime = false
 	params.print_timestamps = false
 	params.print_special = false
-	params.n_threads = C.int(4)
+	params.n_threads = C.int(whisperThreads)
 	params.single_segment = true
 
 	lang := C.CString(req.Lang)
@@ -162,7 +174,7 @@ func (h *whisperHandler) Transcribe(ctx context.Context, req worker.TranscribeRe
 	}
 
 	noSpeechProb := float64(C.whisper_full_get_segment_no_speech_prob(h.ctx, 0))
-	if noSpeechProb > 0.9 {
+	if noSpeechProb > noSpeechFloor {
 		confidence = 0
 	}