tw_vocal joins the mutable class; the PA verified live

The MEDIA_MANIFEST invariant fired on its second real deploy and was right again: sing.py re-sings found/tw_vocal.mp3 on every offline render under a fixed name — mutable by nature, so it joins the manifests in the no-cache class (excluded from the invariant set

• Production-verified end to end: headless chromium parked the travel loop on transitwave at https://stellate.app

▶ Play it: Rail Replacement Rapture — parked on the genre this change names https://stellate.app/?genre=transitwave&seed=7326&path=749.12536,768.12569,730.12569&xdur=13.122

5f12856 https://github.com/aboard-io/stellate/commit/5f12856e07bfc9e100fbc827cf4525e7f12d00a2