refactor(cli): consolidate input modes into extensible system

- Replace isBashMode/isReferralMode booleans with single inputMode state
- Create input-modes.ts with mode configurations (icon, color, placeholder)
- Simplify chat-input-bar.tsx by removing if/else chains
- Update all mode-related code to use new system
- Makes adding future modes (e.g. debug, search) easier

Author: brandonkachen