Add a ◎ XX% indicator to the CLI status bar showing the prompt cache
hit rate (cache_read / prompt_tokens). This helps users monitor how
effectively their provider's prompt caching is working.
Features:
- Color-coded: green (≥70%), yellow (40-70%), red (<40%)
- Adaptive precision: integer on narrow terminals, one decimal on wide
- Only shown when cache data is available (provider supports it)
- Compatible with OpenAI, Anthropic, DeepSeek, xiaomi, and other
providers that return prompt_tokens_details.cached_tokens
Tests: 6 new test cases, 43/43 passing
Cheri Wen