Feature: ship a working Command Code provider in the login window

Request
Add Command Code as a first-class, working provider that ships with jcode and appears in the /login window, built and maintained by the maintainer.

Why
A local/uncommitted commandcode integration exists in a user fork, but it does not work properly and is not part of any jcode release. Rather than a partial third-party build, this should be authored and shipped upstream so it works out of the box for everyone.

Suggested wiring (from the local attempt)

• OpenAI-compatible profile id commandcode
• api base https://api.commandcode.ai/provider/v1
• api key env COMMANDCODE_API_KEY, env file commandcode.env
• setup url https://commandcode.ai
• Login provider descriptor with display name Command Code, API-key auth, and inclusion in tui_login_providers() so it shows in /login.

Acceptance criteria

• Command Code appears as a selectable provider in the /login window (and CLI) in a released build.
• Authenticating with a COMMANDCODE_API_KEY works end to end (models listed, chat completes).
• /usage reports sensible data for the provider (not just a /models key-status probe).

Please build and ship this provider so users do not have to rely on an uncommitted fork build.

Start at tui_login_providers() and the /login entry point, then trace the provider path used by the CLI and /usage. Add the Command Code configuration described in the issue and verify that the provider appears in a released build, authenticates with COMMANDCODE_API_KEY, lists models, completes chat, and reports meaningful usage data.