Support configurable provider ID and server-authoritative catalogs

[RaviTharuma]

Closes #1

Summary

• make the provider/auth namespace configurable while retaining cliproxy as the default
• optionally request CLIProxyAPI's rich client_version catalog and treat its metadata as authoritative
• preserve every valid server-advertised reasoning level, including ultra, as an effective reasoningEffort variant
• allow fabricated built-in fallback models to be disabled independently of stale live cache fallback
• keep external models.json and models.dev enrichment independently disableable

Validation

• npm test (33 tests)
• npm run build
• npm run check:exports