Rebrand to SegVision Engine, remove AI terminology, and fix video download extension headers

fix: resolve 'Failed to fetch' by hardening API URL detection and using same-origin relative paths

fix: restore missing FastAPI and Typing imports in app_hf.py

fix: explicit sys.path update to resolve inference module import error at runtime

fix: unified deployment fix with flat routing, Suspense boundaries, and forced static export

refactor: drop nginx+standalone, use static export served by FastAPI on :7860

chore: add HF Spaces Docker deployment

chore: remove pycache, env files and lock files

Initial commit — SegVision Video Segmentation App