scenes: three backdrops pointed at sources that no longer exist

Mid-soundcheck, 17:40: the decolle backdrop stayed up through Salut Nu and
Chere Mireille. Not a stale scene — Chere Mireille does declare one, and it
parses fine quoted or bare. Its FILE was gone: both PerfectSunriseLoop.gif
and rose_bloom.gif had been cleaned out of ~/Downloads, so the resolver
returned nothing and the HUD kept painting the last scene that worked.

The converted mp4s were never lost — they live in visuals/scenes, which is
where scene-ingest writes them. Repointed chere_mireille, sept1 and
rose_rouge at those, by absolute path: an mp4 passes the guard as video with
no size limit and no derived-twin lookup, where the raw gif would have been
refused anyway (decolle.gif is 797MB).

Downloads is a staging area, not a source of truth. A backdrop that lives
there dies the next time it is tidied.

live/collab/baba/sept1.tidal

--- url: "/home/pln/Downloads/PerfectSunriseLoop.gif"
+-- url: "/home/pln/Work/Sound/Tidal/visuals/scenes/PerfectSunriseLoop.mp4"
 
 -- À Mon Amour
 -- <3

live/midi/nova/nujazz/chere_mireille.tidal

--- /home/pln/Downloads/PerfectSunriseLoop.gif
+-- url: "/home/pln/Work/Sound/Tidal/visuals/scenes/PerfectSunriseLoop.mp4"
 -- Chère Mireille,
 -- <3
 do

live/midi/nova/nujazz/rose_rouge.tidal

 resetCycles
 
--- url: "/home/pln/Downloads/rose_bloom.gif"
+-- url: "/home/pln/Work/Sound/Tidal/visuals/scenes/rose_bloom.mp4"
 -- audition les autres traitements: -- scene: rose_bloom_fast | rose_bloom_rebloom | rose_bloom_noir
 
 -- LE JAZZ C'EST QUOI???