Adds a live quota gauge for the z.ai ZCode coding plan on all three surfaces: the CLI plan view, the desktop Plans page, and the mac menu bar. It reads the provider's own remaining-allowance endpoint, so it is quota-only and touches no cost or spend paths. One decoder is shared between Z.ai and ZCode, and ZCode is hidden when a Z.ai login already covers the same endpoint. The fetch is bounded with graceful disconnected, waiting and error states, and no socket is opened without a login. The logo shows on every surface, and ZCode is listed in the desktop supported-provider list to match the menu bar catalog.
