providers: add MiniMax preset

[octo-patch]

What Changed

• Add a MiniMax provider preset and default credential mapping.
• Route the default runtime and Murph runtime to their protocol-specific MiniMax endpoints, with configuration overrides for both supported regions.
• Document MiniMax-M3 and MiniMax-M2.7 context, modalities, thinking, pricing, and endpoint selection.
• Cover provider parsing, metadata credentials, model mappings, runtime environment generation, and regional endpoint overrides.

Why

Phantom did not have a built-in MiniMax registry entry, so users had to assemble equivalent custom configuration manually.

How I Tested

• bun test (2,648 passed, 10 skipped, 1 todo)
• bun run lint
• bun run typecheck
• A local Agent SDK request capture confirmed that an /anthropic base URL produces exactly one /v1/messages suffix.

Checklist

• Tests pass (bun test)
• Lint passes (bun run lint)
• Typecheck passes (bun run typecheck)
• No secrets or .env files included
• No default exports or barrel files added