fix(a11y): Sprint 7 — semantic HTML and accessibility deep-dive
S7.1: Replace div onClick with semantic button in DialogTrigger.tsx
S7.2: Replace role="button" divs with native <button> elements in 12 files
(PlaylistCard, TrackCard, ConversationItem, NotificationMenuItem,
AudioPlayerTrackInfo, SearchPageResults, ProjectsManagerAddCard,
ProjectsManagerCard, GearInventoryGrid, UploadModal, dropdown.tsx,
LibraryPageGrid)
S7.3: Add focus-visible:ring-2 to 14 form inputs with outline-none across
9 modal files (CreateGroupModal, DataExportModal, EditPlaylistModal,
AddToPlaylistModal, BanUserModal, RefundRequestModal, FlashSaleModal,
TipStreamerModal, CreatePostModal)
S7.4: Add semantic landmarks — <section> in DashboardPage, <article> in
PostCard and CourseCard
Co-authored-by: Cursor <cursoragent@cursor.com>