feat: audio surfaces (TTS + transcription), imagegen.Editor, llamaswap health probe

- New leaf package `audio` (ADR-0017): SpeechModel/SpeechProvider and
  TranscriptionModel/TranscriptionProvider with imagegen conventions
  (zero value = backend default, functional options + Apply, bytes
  in/out, never URLs). Root re-exports added.
- imagegen.Editor (ADR-0018): optional image-to-image interface —
  EditRequest carries the generation knobs plus Init image and
  denoising Strength; separate interface so existing Models keep
  compiling.
- provider/llamaswap implements all of it: POST /v1/audio/speech (JSON,
  raw-audio response, MIME from Content-Type with format fallback),
  POST /v1/audio/transcriptions (multipart, response_format=json),
  ListVoices (GET /v1/audio/voices?model=, tolerant of string-list and
  object-list shapes), POST /sdapi/v1/img2img (txt2img wire +
  init_images/denoising_strength, shared image decode), and Health(ctx)
  (GET /health) — a cheap liveness probe for often-offline hosts.
- Hermetic httptest coverage for every new wire shape and validation
  path; README sections + support-matrix footnote updated in the same
  commit (also corrects the stale /v1/images/generations claim — the
  image path has been SDAPI since the seed fix).

First consumer: mort's llamaswap media tool cluster (status / image /
TTS / STT agent tools against the netherstorm host).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AXQxVhXBw8PwFAtsVrXSmj

progress.md

@@ -248,3 +248,19 @@ alias-in-chain failover, permanent-policy override) and wires anything the
 tests flush out.
 
 **Next:** Phase 2 — exhaustive health/chain test matrix.
+
+## 2026-07-11 — audio surfaces + image editing (ADR-0017, ADR-0018)
+
+- New leaf package `audio`: `SpeechModel`/`SpeechProvider` (TTS) and
+  `TranscriptionModel`/`TranscriptionProvider` (STT), imagegen conventions
+  (zero value = backend default, options + Apply, bytes in/out). Root
+  re-exports added.
+- `imagegen.Editor` — optional img2img interface (`EditRequest` with
+  `Init Image` + `Strength`); shared `Result`.
+- provider/llamaswap implements all of it: `/v1/audio/speech`,
+  `/v1/audio/transcriptions` (multipart), `ListVoices`
+  (`/v1/audio/voices?model=`, shape-tolerant), `/sdapi/v1/img2img`
+  (txt2img wire + init_images/denoising_strength, shared decode), and a
+  cheap `Health(ctx)` probe (GET /health) for often-offline hosts.
+- Hermetic httptest coverage for every new wire shape + validation errors.
+- Consumer: mort's llamaswap media tool cluster (status/image/TTS/STT tools).