pi tui style code agent base on deepseek harness

Key features

• Terminal-native workflow — streaming Markdown, five-line collapsed reasoning and verbose tool bodies, always-visible line-numbered file diffs, selectable/copyable results, themed paste markers, shell blocks, and a bottom-pinned composer.
• TUI renderer and interaction inspiration: Pi
• Standard and PTC modes — Standard makes direct tool calls
• PTC composes multi-step work in one TypeScript program.
• PTC child calls use native tool rows, with long bodies collapsed and file diffs always visible.