v0.6.0 — balance-only core
Sidebar shows ONLY the real account balance from the official /user/balance endpoint.
- Estimate engine removed (token_usage reports exact tokens + real balance)
- BalanceClient: request dedup, 5s→5m backoff, stale-cache serving
- Widget: unavailable/stale/low-balance states, hidden-tab pause
- Storage schemaVersion 3 (balance samples survive migration)
- Config: lowBalanceAlert (default 5)