feat: add MiniMax M3 model support

[octo-patch]

This cleanly replaces #8401.

Describe Your Changes

• Add MiniMax-M3 to the built-in MiniMax model and capability registries with streaming, tools, and vision support.
• Keep MiniMax-M2.7 available with its documented 204.8K context window.
• Derive the Anthropic API version path inside the adapter so users configure the documented /anthropic base URL while requests reach /v1/messages.
• Document global and CN OpenAI-compatible and Anthropic-compatible endpoint setup.

Test Plan

• corepack yarn vitest run --project @janhq/web-app web-app/src/lib/__tests__/models.test.ts web-app/src/lib/__tests__/model-factory.test.ts (81 passed)
• NODE_OPTIONS='--max-old-space-size=4096 --no-experimental-webstorage' corepack yarn vitest run --project @janhq/web-app (2,715 passed)
• corepack yarn lint
• corepack yarn build:web
• cd docs && yarn build
• Captured request URLs for both regions and both API formats.

Screenshots

Not applicable. This changes provider metadata, request routing, tests, and documentation without changing the existing UI layout.

Self Checklist

• Added focused tests.
• Updated documentation.
• Kept the change scoped to MiniMax support.