feat: add AIML API provider support

Introduces AIMLAPI as a supported AI provider, including model list, config validation, and engine implementation. Updates README and engine selection logic to integrate AIMLAPI for chat completions.

Refactor AimlApiEngine response handling

Removed dependency on removeContentTags and simplified message content extraction. Minor header formatting fix for HTTP-Referer. This streamlines the response handling and reduces unnecessary processing.

src/engine/aimlapi.ts

@@ -0,0 +1,47 @@
+import OpenAI from 'openai';
+import axios, { AxiosInstance } from 'axios';
+import { AiEngine, AiEngineConfig } from './Engine';
+
+interface AimlApiConfig extends AiEngineConfig {}
+
+export class AimlApiEngine implements AiEngine {
+  client: AxiosInstance;
+
+  constructor(public config: AimlApiConfig) {
+    this.client = axios.create({
+      baseURL: config.baseURL || 'https://api.aimlapi.com/v1/chat/completions',
+      headers: {
+        Authorization: `Bearer ${config.apiKey}`,
+        'HTTP-Referer': 'https://github.com/di-sukharev/opencommit',
+        'X-Title': 'opencommit',
+        'Content-Type': 'application/json',
+        ...config.customHeaders
+      }
+    });
+  }
+
+  public generateCommitMessage = async (
+    messages: Array<OpenAI.Chat.Completions.ChatCompletionMessageParam>
+  ): Promise<string | null> => {
+    try {
+      const response = await this.client.post('', {
+        model: this.config.model,
+        messages
+      });
+
+      const message = response.data.choices?.[0]?.message;
+      return message?.content ?? null;
+    } catch (error) {
+      const err = error as Error;
+      if (
+        axios.isAxiosError<{ error?: { message: string } }>(error) &&
+        error.response?.status === 401
+      ) {
+        const apiError = error.response.data.error;
+        if (apiError) throw new Error(apiError.message);
+      }
+
+      throw err;
+    }
+  };
+}