//! Interactive cost-breakdown TUI.
//!
//! A tabbed terminal app over the proxy's token ledger: an **Overview** tab (the savings
//! dashboard), a **Sessions** tab (every session grouped agent → project → session with
//! token and dollar totals), and a **Detail** drill-down (context-window occupancy and
//! per-source cost down to each MCP server). Launched by `status`/`monitor` on a TTY;
//! piped or `--json`/`--csv` invocations keep the plain snapshot.