feat: expose Go and Zen usage - #41824

Summary

• add an authenticated Console endpoint for normalized Go quota windows and Zen billing usage
• expose the account data through the OpenCode server at GET /api/usage using the active OpenCode credential
• generate Promise and Effect client methods under client.usage.get()
• return { connected: false } when no OpenCode account is configured and sanitize upstream failures as service-unavailable errors

Validation

• typechecked schema, protocol, core, server, client, and Console app packages
• core OpenCode provider tests (14 passed)
• server usage endpoint test (1 passed)
• client contract tests (26 passed)

Requested by: @kitlangton (Kit via Slack)