feat: add built-in Volcengine Ark provider support (#741)

Add Volcengine Ark as a first-class API key provider with official model presets, endpoint configuration, API key validation, model discovery, connection testing, provider logo, and runtime alias mapping for `ark/*` model IDs.

Made-with: Cursor

Co-authored-by: kingsy <kingsylin@vip.qq.com>

src/app/api/providers/[id]/models/route.js

@@ -149,6 +149,7 @@ const PROVIDER_MODELS_CONFIG = {
     authPrefix: "Bearer ",
     parseResponse: (data) => data.data || []
   },
+  "volcengine-ark": createOpenAIModelsConfig("https://ark.cn-beijing.volces.com/api/coding/v3/models"),
 
   // OpenAI-compatible API key providers
   deepseek: createOpenAIModelsConfig("https://api.deepseek.com/models"),