Add MOSS-TTS voice-clone + translate demo

Translates a short narrator sentence to Spanish (MarianMT) and
synthesizes it in the narrator's cloned voice (MOSS-TTS
Local-Transformer-v1.5), using a reference clip trimmed from demucs's
isolated vocals stem. First working slice of the full audio-translation
pipeline.

Documents two environment gotchas hit on the RTX 3090: the flagship 8B
checkpoint OOMs on 24GB, and torchaudio/torchcodec fails to load without
manually pulling in nvidia-npp-cu12 and fixing LD_LIBRARY_PATH.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Y1oQ4h4WE4R9KRvMQLr5Ey

README.md

@@ -23,5 +23,10 @@ Chain the three demos together on `media-files/` into an end-to-end pipeline:
 3. `tts` — clone the original speaker's voice (from the isolated vocal stem) and synthesize
    the translated text in that voice, then remix with the original instrumental stem
 
-Stem separation and transcription are already working end to end (see `demucs/README.md` and
-`whisperx/README.md`); translation and voice-cloning TTS are not yet implemented.
+All three stages now have a working, if narrow, proof of concept:
+
+- Stem separation (`demucs/README.md`) and transcription (`whisperx/README.md`) run end to end
+  on the full sample clip.
+- Translation + voice-cloning TTS (`tts/README.md`) works for a single short sentence
+  (English → Spanish, cloned onto the isolated narrator voice via MOSS-TTS). Not yet wired up
+  to run over the full transcript or to remix with the instrumental stem.