revert: Dockerfile back to python app.py (gunicorn caused stuck)

deploy: batch update 3 file(s)

update Dockerfile

fix: keyframe images, video clips, evidence images, live stream webcam+URL, remove demo mode

fix: remove llama-cpp-python (C++ build times out on free tier)

fix: prevent CUDA torch re-download and speed up llama-cpp-python build

fix: replace removed Debian trixie packages (libgl1-mesa-glx -> libgl1, libgdk-pixbuf2.0-0 -> libgdk-pixbuf-xlib-2.0-0)

fix: use JSON array form for COPY with spaces in filename

feat: Full DetectifAI backend with B2 storage, DEMO_MODE, Stripe bypass