feat: side-by-side inspection/chat layout + 360° spin interaction

feat(inspection): add panel HTML structure and CSS styles

refactor: replace canvas overlay with SVG-based bounding box system

refactor: remove remaining dead HEL/threat code remnants

feat: add timeline heatmap with detection highlights for Tab 2 video player

feat: bidirectional click-to-select between video overlay and track cards

Redesign track cards with inline features, remove separate features panel, clean up overlays

Reduce left sidebar by 50% and move track cards to right of video

ui: Make video frame full-width, move features beside track cards

feat: Add threat chat feature for Q&A about detected threats

feat: Continuous object tracking, speed estimation, and overlay syncing

Refactor frontend into modular ES modules in frontend/ folder