feat(narration): add FishAudio as a selectable TTS provider

[fancyboi999]

Closes #53

What

Adds FishAudio alongside MiniMax as a narration (voiceover) backend, selectable per workspace in Studio → Settings → Audio. Background music stays MiniMax-only (FishAudio has no music generation).

Why

We use FishAudio TTS heavily (custom reference_id voices), but the studio's narration pipeline was MiniMax-only. See #53 for motivation.

Changes

• core: new fishaudio.ts — resolveFishAudioCredentials / generateFishTts / listFishVoices — plus a shared TtsAudioResult type and 16 unit tests.
• config: MediaConfigStore gains FishAudio creds + a narrationProvider setting; the speech model is env-controlled (FISH_AUDIO_MODEL, default s1).
• server: narration routes by provider; new /api/config/fishaudio, /api/config/narration-provider, /api/fishaudio/voices (the key stays server-side — the browser never sees it).
• studio UI: provider toggle + FishAudio key pane (single host, no region); a searchable voice picker (reference_id) with sample preview; en + zh strings.

Design doc: research/2026-06-15-spec-10-fishaudio-tts-provider.md (RFC-10).

Provider differences absorbed

	MiniMax	FishAudio
Model select	body field	model header (env-driven)
Response	JSON + hex envelope	raw binary stream
Voices	6 fixed voice_id	account reference_id (searchable)
Region	intl / CN split	single global host
Music	yes	none (stays MiniMax)

Screenshots

Verification (real, not mocks)

• Unit: pnpm --filter @html-video/core test → 16/16.
• Real API: generateFishTts → real MP3 (ffprobe-valid); listFishVoices → account models.
• Studio E2E: configure key → switch provider → search + pick a voice → synthesize → asset created; export muxes the FishAudio narration into the MP4 — ffprobe shows h264 video + aac audio, and ffmpeg -f null - decodes clean.
• Regression: cli 14/14, runtime 4/4, adapter-remotion 8/8, smoke all green; the MiniMax narration path is unchanged (only a creds variable rename).

Notes

• A pre-existing adapter-hyperframes test script points at a missing test/ dir (unrelated to this change; present on main).
• MiniMax actual generation wasn't re-run here (no key on hand); its routing + the graceful "key not configured" message were verified.

[lefarcen]

Hey @fancyboi999! 👋

Nice work on the FishAudio integration — the design doc + comprehensive testing (16 unit tests + real API verification + E2E export validation) gives a clear picture of what's changing. The provider abstraction looks clean, and keeping the server-side key handling is the right security move.

I've assigned this to @mrcfps for code review. A few things that look promising from the structure:

• The credential resolution pattern mirrors MiniMax (env fallback + server-side only)
• Provider differences are absorbed cleanly (model header vs body, binary stream vs JSON envelope)
• The searchable voice picker is a nice UX touch for reference_id accounts

Related context: #45 discusses provider selection patterns, and #38 (SenseAudio) has overlapping config/UI seams worth checking for consistency.

Once @mrcfps reviews, we'll move this forward. Let me know if anything's unclear!

💡 To drive this PR to merge hands-free, paste this to your AI coding agent (Claude Code / Codex / opencode / Cursor …):
Take over nexu-io/html-video#54 until it merges — read https://raw.githubusercontent.com/nexu-io/looper/main/skills/pr-takeover/SKILL.md and follow it.

[fancyboi999]

Closing this for now to keep the PR queue current after the review has been pending for about a month.

The implementation branch will remain available. If the maintainers would like to continue with FishAudio support, please comment here or reopen the PR. I am happy to rebase it onto the latest main branch, address review feedback, and rerun the API, unit, and end-to-end validation.

[lefarcen]

Hey @fancyboi999 — thanks for the clear heads-up, and thanks again for putting this together. The FishAudio direction, the validation notes, and the offer to keep the branch available are all genuinely helpful context for us.

Closing it here makes sense given the review delay. If we decide to pick up FishAudio support again, we’ll comment here or reopen the PR and continue from your branch. Appreciate you leaving the door open to rebase and rerun validation. ❤️