✨ add openrouter AI provider support with comprehensive model list

Add OpenRouterEngine class and integrate it into the configuration
system. OpenRouter provides access to 300+ AI models through a
unified API, expanding model availability for commit message
generation beyond existing providers.

src/engine/openrouter.ts

@@ -0,0 +1,49 @@
+import OpenAI from 'openai';
+import { AiEngine, AiEngineConfig } from './Engine';
+import axios, { AxiosInstance } from 'axios';
+import { removeContentTags } from '../utils/removeContentTags';
+
+interface OpenRouterConfig extends AiEngineConfig {}
+
+export class OpenRouterEngine implements AiEngine {
+  client: AxiosInstance;
+
+  constructor(public config: OpenRouterConfig) {
+    this.client = axios.create({
+      baseURL: 'https://openrouter.ai/api/v1/chat/completions',
+      headers: {
+        Authorization: `Bearer ${config.apiKey}`,
+        'HTTP-Referer': 'https://github.com/di-sukharev/opencommit',
+        'X-Title': 'OpenCommit',
+        'Content-Type': 'application/json'
+      }
+    });
+  }
+
+  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;
+      let content = message?.content;
+      return removeContentTags(content, 'think');
+    } catch (error) {
+      const err = error as Error;
+      if (
+        axios.isAxiosError<{ error?: { message: string } }>(error) &&
+        error.response?.status === 401
+      ) {
+        const openRouterError = error.response.data.error;
+
+        if (openRouterError) throw new Error(openRouterError.message);
+      }
+
+      throw err;
+    }
+  };
+}