Rename project from Zenbox to Mobile Client

update ui color + padding

feat(ui): add divider to separate responses

feat(ui): remove background color for type bar

feat(ui): render markdown text in MessageBubble

refactor(ui): update surface and item background colors to light gray

refactor(ui): change theme toggle to dropdown selection with Light/Dark options

feat(ui): add back button to ChatScreen for navigation

fix(ui): add background color to send button so it's always visible

feat(ui): add settings page for configuring default model for new chat sessions

feat(ui): add dark mode theme support with ThemeToggle component

fix(chat): eliminate empty lines between AI messages

docs(readme): add comprehensive project documentation

fix(chat): display user messages immediately when sent

feat(chat): add model selection feature with search