chore: update CHANGELOG for /stats dashboard and Z AI provider

Author: elkaix

CHANGELOG.md

@@ -15,6 +15,9 @@ GitHub Releases page; `0.8.0` is the new starting line.
 
 ## Unreleased
 
+- **`/stats` usage dashboard.** New slash command opens an interactive prompt_toolkit TUI showing token and cost breakdown by provider/model across Today / This Week / Last Week / All Time. Powered by a static pricing table (`get_cost_usd`) and a session collector that walks `~/.pythinker/sessions/` wire files. `StatusUpdate` wire events now carry optional `model_name` / `provider_key` fields for per-step attribution.
+- **Z AI provider auth.** Login/logout via API key, model discovery, and OAuth selector wired into the TUI and `refresh_managed_models`.
+
 ## 0.33.0 (2026-06-03)
 
 ### What changed in this release