V2 - TaskFlow

Add Docker + overhaul UI, JS, and styles

Introduce Docker deployment (Dockerfile, .dockerignore, docker-compose.yml) and add repo banner asset. Revamp the app into "TaskFlow": large UI/UX redesign (index.html, style.css) with glassmorphic cards, theme toggle, analytics widgets, search/filters, priority/category badges and an edit modal. Refactor client logic (script.js) into a modern stateful implementation: centralized tasks state, CRUD (add/edit/delete), sorting, filtering, search, stats update, theme persistence, animations and LocalStorage persistence. Update README to reflect new branding, features and run instructions.