Refresh MiniMax defaults

[octo-patch]

Reason: refresh MiniMax defaults to MiniMax-M3 and current endpoints.

Summary

• Set MiniMax provider suggestions to default to MiniMax-M3 in the model wizard.
• Added MiniMax Anthropic-compatible choices for global and domestic endpoints using SDK-compatible /anthropic base URLs.
• Kept the existing OpenAI-compatible endpoints current for both regions.
• Added regression coverage that verifies the SDK constructs exactly one /v1/messages path.

Test plan

• bun run check (228 tests)
• git diff --check

[octo-patch]

I updated the MiniMax Anthropic-compatible base URLs to the SDK-compatible /anthropic roots, so requests now resolve to exactly one /v1/messages path. I added regression coverage for both regions and the two configured model IDs; bun run check passes with 228 tests.

[octo-patch]

Superseded by #51, rebuilt from the latest main with clean commit metadata. The replacement includes the corrected SDK-compatible base URLs and regression coverage: #51