[Feature]: Xiaomi Mimo 2.5 TTS request

### Problem or Motivation

Currently, there is no native support for Xiaomi MiMo TTS in OpenMAIC. When attempting to add it via the generic Custom TTS provider, the test fails with a "Not Found" error.

This happens because the custom provider assumes a standard OpenAI format and automatically routes requests to the /v1/audio/speech endpoint. However, the Xiaomi MiMo API handles text-to-speech differently: it processes audio generation through the /v1/chat/completions endpoint by passing a specific audio object in the payload. This structural difference makes it impossible to use MiMo's high-quality TTS models (like mimo-v2.5-tts) as a simple drop-in replacement via the existing custom provider interface.

### Proposed Solution

I propose adding native provider support for Xiaomi MiMo TTS. This would require:

Dedicated UI Provider: Adding a "Xiaomi MiMo TTS" option in the Text-to-Speech provider list.

Endpoint Routing: Routing the API requests for this specific provider to the /v1/chat/completions endpoint instead of the standard /audio/speech path.

Payload Formatting: Adjusting the request payload to include the required audio object format as per Xiaomi's official API documentation.

Model Support: Adding support for MiMo-specific TTS models (e.g., mimo-v2.5-tts, mimo-v2-tts) and allowing users to configure valid voice parameters (such as 茉莉).

### Alternatives Considered

_No response_

### Area

TTS / Voice

### Additional Context

_No response_