feat: add support for DouBao, Ernie, Kimi, Qwen, ZhiPu LLM providers

Introduces new provider modules for DouBao, Ernie, Kimi, Qwen, and ZhiPu, and registers them in the LLM registry. Updates documentation and .env.example to include configuration instructions for these providers. Refactors OpenAI provider to support OpenAI-compatible endpoints. Adds @ai-sdk/openai-compatible and node-fetch dependencies.

app/lib/modules/llm/providers/openai.ts

@@ -1,4 +1,5 @@
 import { createOpenAI } from '@ai-sdk/openai';
+import { createOpenAICompatible } from '@ai-sdk/openai-compatible';
 import type { LanguageModel } from 'ai';
 import { BaseProvider } from '~/lib/modules/llm/base-provider';
 import type { ModelInfo } from '~/lib/modules/llm/types';
@@ -42,13 +43,19 @@ export default class OpenAILikeProvider extends BaseProvider {
       throw new Error(`Missing configuration for ${this.name} provider`);
     }
 
-    let openaiBaseUrl = baseUrl;
-    if (!baseUrl) {
-      openaiBaseUrl = undefined;
+    if (!!baseUrl) {
+      const provider = createOpenAICompatible({
+        name: this.name,
+        baseURL: baseUrl,
+        apiKey,
+        includeUsage: true,
+      });
+
+      return provider(model);
     }
 
     const openai = createOpenAI({
-      baseURL: openaiBaseUrl,
+      baseURL: baseUrl,
       apiKey,
     });