feat: add MiniMax image generation

[octo-patch]

Reason: The built-in image-generation tool does not support MiniMax models or either official regional endpoint.

This change adds the MiniMax image model catalog, provider-backed global and China endpoint selection, native request and response handling, model availability settings, and the generate_minimax_image built-in tool. The focused adapter tests cover global URL responses, China endpoint base64 responses, and provider errors.

Checks:

• git diff --check
• bun test packages/runtime/tests/models/minimax-image-generation.test.ts
• bun run check:changed

[foreleven]

Hi @octo-patch, this PR currently has merge conflicts with main. Could you please update the branch with the latest main and resolve the conflicts? Thanks!

[octo-patch]

Thanks for flagging this. I merged the latest main into this branch and resolved the single conflict in packages/runtime/src/tools/built-in/media.ts, keeping both the image-saving helpers from main and the MiniMax numeric-argument validation helper. I ran the runtime test suite (105 pass), tsc --noEmit on the root, runtime, ui, desktop and server projects, and eslint on the touched files. The branch is conflict-free now and CI is green.