v0.5.1

Added

• ExRatatui.Widgets.Markdown — markdown rendering widget with syntax-highlighted code blocks, powered by tui-markdown (pulldown-cmark + syntect)
• ExRatatui.Widgets.Textarea — multiline text editor with undo/redo, cursor movement, and Emacs-style shortcuts. Second stateful widget — state lives in Rust via ResourceArc
• ExRatatui.Widgets.Throbber — loading spinner widget with 12 animation sets (braille, dots, ascii, arrow, clock, and more)
• ExRatatui.Widgets.Popup — centered modal overlay widget for dialogs, confirmations, and command palettes
• ExRatatui.Widgets.WidgetList — vertical list of heterogeneous widgets with selection and scrolling, ideal for chat message histories
• ExRatatui.Widgets.SlashCommands — slash command parsing, matching, and autocomplete popup rendering
• Textarea NIF functions: textarea_new/0, textarea_handle_key/3, textarea_get_value/1, textarea_set_value/2, textarea_cursor/1, textarea_line_count/1
• Example: chat_interface.exs — AI chat interface demonstrating Markdown, Textarea, Throbber, Popup, WidgetList, and SlashCommands

Fixed

• Replaced deprecated Padding::zero() with Padding::ZERO in Rust widget renderers
• Wired up unused style field in WidgetList render function (was #[allow(dead_code)])
• Fixed flaky Rust throbber step test — calc_step(0) uses random index, now tests with deterministic non-zero steps
• Throbber animation set test now covers all 12 sets (was 7)