fix: track cards update during playback + periodic GPT re-analysis

feat: add detailed timing metrics to GroundedSAM2 segmenter

feat: add job processing timing and latency measurements to backend and frontend

feat(frontend): improve UI for detection and chat interaction

Refactor GPT sync in client.js: extract _syncGptFromDetections and add final sync on job completion

Fix track cards stuck at UNASSESSED due to frontend race condition

Refine GPT enrichment logic, add relevance badges to UI, and fix minor model/logging issues

Async GPT enrichment: fire-and-forget background task updates track cards from UNASSESSED to ASSESSED

Update overlays, tracker, GPT reasoning, and threat chat improvements

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