Three UX improvements for interactive mode:
1. Input prompt: Shows '»' (bold cyan) on stdin before reading user input
2. Output prefix: Agent responses prefixed with 'G>' (bold green)
3. Thinking indicator: Animated spinner on stderr showing 'answering (N.Ns)'
with braille frame characters, auto-clears when response arrives
- Start/stop via tokio::sync::watch channel + tokio::spawn
- Only shows when interactive (atty detection)
- Does not affect gateway/sub-agent modes
Tara Menon
1d8e26e683