[codex] Unify Studio service model picker sources

[whh110112]

Summary

• Route the Studio /api/v1/services/models endpoint through listModelsForService so the chat/write model picker uses the same live/enriched model resolver as service detail flows.
• Add MiniMax-M3 to the MiniMax fallback model bank and legacy known model list.
• Update regression coverage for the unified service model resolver path and MiniMax fallback ordering.

Root cause

The service detail/test flow can see refreshed provider models, but the chat/write model picker was fed by /services/models, which only read each provider's static ep.models bank. That let configured/new provider models drift from the writing surface.

Validation

• Compared the PR branch against Narcooo/inkos:master; diff is one commit touching the intended 5 files.
• Local test execution was not run because this environment could not complete a repository clone; the patch was applied through GitHub's Git Data API after targeted source inspection.