Add a new Sidebar component and integrate it into App.tsx (replacing Header), updating overall layout to a two-column flex layout and moving/footer adjustments. Substantially refactor DetailView: new responsive layout, progress bar, tabbed navigation (Overview, Cast, Tracks, Seasons, etc.), improved cast and tracks UI, various icon and metadata display tweaks, and several UX/responsiveness fixes. Also add AGENTS.md (project development guide) and minor related imports/cleanup across changed files.
