feat: add MiMo (Xiaomi) as AI provider (#887)

* feat: add MiMo (Xiaomi) as AI provider

* fix: correct MiMo default base URL, suggested models, and reasoning support

- Default base URL was the China Token Plan endpoint (tp- keys only);
  switch to https://api.xiaomimimo.com/v1 which works with standard
  pay-as-you-go sk- keys. Token Plan users can override in settings.
- Replace deprecated mimo-v2-flash suggestion with mimo-v2.5
  (v2 series was deprecated on 2026-06-30).
- Use createDeepSeek instead of createOpenAI so reasoning_content is
  passed back during multi-turn tool calls (MiMo returns 400 without
  it), matching the existing Kimi implementation.
- Add mimo to SINGLE_SYSTEM_PROVIDERS so system messages are merged.
- Fold validate-model case into the shared OpenAI-compatible group.
- Drop the Bot icon special case; models.dev serves a real xiaomi logo
  via PROVIDER_LOGO_MAP.
- Document MIMO_API_KEY/MIMO_BASE_URL in env.example and
  docs/{en,cn,ja}/ai-providers.md.

* feat: show base URL hint for MiMo in provider settings

MiMo has two endpoints tied to key type: pay-as-you-go keys (sk-...)
use the default api.xiaomimimo.com/v1, while Token Plan keys (tp-...)
require token-plan-cn.xiaomimimo.com/v1. Surface this under the Base
URL field like the existing MiniMax hint, in all four locales.

---------

Co-authored-by: mapengfei <mapengfei@srsj.com>
Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

lib/types/model-config.ts

@@ -23,6 +23,7 @@ export type ProviderName =
     | "kimi"
     | "minimax"
     | "novita"
+    | "mimo"
 
 // Individual model configuration
 export interface ModelConfig {
@@ -114,6 +115,7 @@ export const PROVIDER_LOGO_MAP: Record<string, string> = {
     modelscope: "modelscope",
     minimax: "minimax",
     novita: "novita",
+    mimo: "xiaomi",
 }
 
 // Provider metadata
@@ -200,6 +202,10 @@ export const PROVIDER_INFO: Record<
         label: "Novita AI",
         defaultBaseUrl: "https://api.novita.ai/openai",
     },
+    mimo: {
+        label: "MiMo (Xiaomi)",
+        defaultBaseUrl: "https://api.xiaomimimo.com/v1",
+    },
 }
 
 // Suggested models per provider for quick add
@@ -437,6 +443,7 @@ export const SUGGESTED_MODELS: Partial<Record<ProviderName, string[]>> = {
         "moonshotai/kimi-k2.6",
         "deepseek/deepseek-v4-flash",
     ],
+    mimo: ["mimo-v2.5-pro", "mimo-v2.5"],
 }
 
 // Helper to generate UUID