Reveil Canon fiabilise : poll USB au lieu de sleep fixe, retry gphoto2, frontend patient

Backend: reveiller_canon() poll USB toutes les 1s (max 20s) au lieu de sleep(15+25),
3 tentatives gphoto2, temps total 10-30s au lieu de 40s fixe.
Frontend: attend 40s meme si reveil_en_cours=false (reconnexion auto),
messages plus clairs ("Touchez l'ecran et reessayez").

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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