Pitch

DeepSeek-unique. We did the work in v0.8.4 (#287, #289, #290, #291, #292) to stabilise V4's prefix cache so users get the 90% discount. `/cache` shows the hit-rate table on demand. Make it visible per-turn so users see the cost savings live: a small footer chip reads `cache 87%` after each turn settles.

Coloring:

• ≥ 80%: STATUS_OK green
• 60-79%: muted
• < 60%: STATUS_WARN — something might have churned the cache

Click / hover (when #375 right-click ships) opens the full `/cache` table.

Acceptance

• Footer chip reflects the most recent turn's cache hit %.
• Color matches the threshold rules.
• No chip when cache telemetry isn't available (early turns, offline, etc.).