Init photobooth - borne photo evenementielle RPi4

Backend FastAPI complet : camera gphoto2, filtres/overlays Pillow,
chroma key OpenCV, multi-shot/collage, GIF, impression CUPS, email SMTP,
QR code. Frontend web vanilla (HTML/CSS/JS) pour Chromium kiosk.
Menu admin cache (appui long coin ecran). Toutes les fonctionnalites
activables/desactivables. Scripts install + systemd pour RPi4.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/requirements.txt

@@ -0,0 +1,11 @@
+fastapi==0.115.0
+uvicorn[standard]==0.30.0
+python-gphoto2==2.5.0
+Pillow==10.4.0
+imageio==2.35.0
+opencv-python-headless==4.10.0.84
+qrcode[pil]==7.4.2
+pycups==2.0.4
+python-multipart==0.0.9
+aiofiles==24.1.0
+websockets==12.0