feat: wave-3 audio surfaces — stems, sfx, speech enhance, voice clone, translate (ADR-0024)

- audio.StemSeparator/StemSeparationProvider: Demucs zip transport via
  POST /upstream/<id>/v1/stems (Mode two -> two_stems=vocals; model +
  format fields); bounded zip unpack, entry name -> stem, ext -> MIME.
- SFXModel reuses musicgen against the sync /upstream/<id>/v1/sfx route
  (JSON prompt/seconds/steps/cfg_scale/seed -> WAV); musicgen.Request
  gains CFGScale.
- audio.SpeechEnhancer/SpeechEnhancementProvider:
  POST /upstream/<id>/v1/enhance -> WAV (result reuses SpeechResult).
- SpeechRequest.ReferenceAudio/ReferenceMIME (+WithReferenceAudio):
  llamaswap switches to the chatterbox clone route
  POST /upstream/<id>/v1/audio/speech/upload (input + voice_file),
  wav MIME fallback.
- TranscriptionRequest.Translate (+WithTranslate): translate=true form
  field, language=auto forced when no explicit hint (whisper.cpp default
  en would skip translation).
- httptest contract tests (zip unpack, clone-route switch, translate +
  auto-language injection); ADR-0024 (index row deferred — MJ-A backfills
  the ADR index table and parallel edits would conflict).

Co-Authored-By: Claude Fable 5 <[email protected]>

provider/llamaswap/enhance.go

@@ -0,0 +1,61 @@
+// enhance.go implements audio.SpeechEnhancementProvider against a
+// DeepFilterNet shim (audioutils) reached through llama-swap's /upstream
+// passthrough (ADR-0024):
+//
+//	POST /upstream/<id>/v1/enhance   multipart file -> WAV
+package llamaswap
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	"gitea.stevedudenhoeffer.com/steve/majordomo/audio"
+	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
+)
+
+// SpeechEnhancerModel implements audio.SpeechEnhancementProvider. The id
+// selects which upstream llama-swap loads.
+func (p *Provider) SpeechEnhancerModel(id string, opts ...audio.SpeechEnhancerModelOption) (audio.SpeechEnhancer, error) {
+	if err := p.requireBaseURL(); err != nil {
+		return nil, err
+	}
+	_ = audio.ApplySpeechEnhancerModelOptions(opts)
+	return &speechEnhancerModel{p: p, id: id}, nil
+}
+
+type speechEnhancerModel struct {
+	p  *Provider
+	id string
+}
+
+// Enhance implements audio.SpeechEnhancer. The endpoint always answers WAV.
+func (m *speechEnhancerModel) Enhance(ctx context.Context, req audio.EnhancementRequest, opts ...audio.EnhancementOption) (*audio.SpeechResult, error) {
+	req = req.Apply(opts...)
+	if len(req.Audio) == 0 {
+		return nil, fmt.Errorf("%w: speech enhancement requires audio bytes", llm.ErrUnsupported)
+	}
+	path, err := upstreamPath(m.id, "/v1/enhance")
+	if err != nil {
+		return nil, err
+	}
+	body, contentType, err := buildMultipart("build enhance form",
+		filePart{field: "file", filename: transcriptionFilename(req.Filename, req.MIME), data: req.Audio},
+		nil)
+	if err != nil {
+		return nil, err
+	}
+	raw, respType, err := m.p.doRaw(ctx, http.MethodPost, path, m.id, contentType, body, maxResponseBytes)
+	if err != nil {
+		return nil, err
+	}
+	if len(raw) == 0 {
+		return nil, &llm.APIError{Provider: m.p.name, Model: m.id, Message: "enhance response contained no audio"}
+	}
+	mimeType := audioResultMIME(respType, raw)
+	if mimeType == "" {
+		return nil, &llm.APIError{Provider: m.p.name, Model: m.id,
+			Message: fmt.Sprintf("enhance response is not audio (Content-Type %q): %s", respType, truncateForError(raw))}
+	}
+	return &audio.SpeechResult{Audio: raw, MIME: mimeType}, nil
+}