Add MiniMax regional API presets

[octo-patch]

Reason: Add direct MiniMax API presets for current models and regional endpoints.

Changes:

• Add global and China presets for both compatible API protocols.
• Seed MiniMax-M3 and MiniMax-M2.7 as the fallback models for each preset.
• Add route coverage for the regional endpoints and model defaults.

Checks:

• git diff --check origin/main...HEAD

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[chatgpt-codex-connector]

Route MiniMax Anthropic model discovery through /v1

When users choose either MiniMax Anthropic preset and click Test or force-refresh models, the routes call buildModelsUrl(), which currently concatenates the preset base with /models; with this base that becomes https://api.minimax.io/anthropic/models instead of MiniMax's Anthropic-compatible model-list endpoint under /anthropic/v1/models. Generation still works because the runner inserts /v1/messages, but model discovery/test fails for the new Anthropic presets unless the stored base includes /v1 internally or buildModelsUrl() adds it for Anthropic bases.

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