Overhaul CLI coder terminal UI/UX and interactive approval workflow

[Matlan1]

Summary

• Add a scrollback-safe inline spinner (Display.spinner / update_spinner / stop_spinner) during TTFT, hidden <tool_call> streaming, and tool execution.
• Stream live line- and character-count progress when the model emits large write_file or edit_file payloads inside hidden <tool_call> blocks.
• Stop printing streamed assistant responses a second time as a Markdown panel after completion.
• Cap new-file creation previews in Display.print_diff to 20 lines with a summary hint instead of dumping full files line by line, and cap edit diffs to 30 lines.
• Expand file and command confirmation prompts ([y/N/a=always/f=full] for files, [y/N/a=always] for commands) with optional rejection feedback routed back to the agent.
• Surface compact error excerpts in normal mode when a tool fails instead of hiding all output behind --verbose.
• Render set_todos as a color-coded terminal checklist and support inline @path / @path:start-end context mentions plus multi-line paste coalescing in the REPL.