headers: {
  "api-key": apiKey,
  "Content-Type": "application/json"
}
`\

This works for the pay-as-you-go endpoint but returns **401 Invalid API Key** for Token Plan users, because `token-plan-cn.xiaomimimo.com` only accepts standard OpenAI-compatible `Authorization: Bearer` auth.

Verified with direct `curl` calls:
- `api-key` header → `token-plan-cn` → **401 Invalid API Key**
- `Authorization: Bearer` → `token-plan-cn` → **200 OK, audio returned**

Since the pay-as-you-go endpoint (`api.xiaomimimo.com`) also accepts `Authorization: Bearer`, switching to Bearer would be backward-compatible.

## Suggested Fix

Change the auth header from `api-key` to `Authorization: Bearer` in the Xiaomi TTS provider:

```diff
 headers: {
-  "api-key": apiKey,
+  "Authorization": `Bearer ${apiKey}`,
   "Content-Type": "application/json"
 }
`\

This maintains compatibility with the pay-as-you-go endpoint while enabling Token Plan (Orbit) users to use MiMo TTS natively.

## Impact

Token Plan users are a rapidly growing segment — the Orbit plan distributed 100T tokens in 30 days to global developers. Without this fix, users on the Token Plan cannot use Xiaomi MiMo as a TTS provider in OpenClaw despite having valid, working credentials.