feat(providers): added openrouter support

This PR is adapted from namanbnsl's original
at https://github.com/namanbnsl/Perplexica/tree/add-openrouter-support

Added minor modifications to bring the openrouter support in line
with the changes in this forked repo

src/lib/providers/openrouter.ts

@@ -0,0 +1,65 @@
+export const PROVIDER_INFO = {
+  key: 'openrouter',
+  displayName: 'OpenRouter',
+};
+import { ChatOpenAI } from '@langchain/openai';
+import { getOpenrouterApiKey } from '../config';
+import { ChatModel } from '.';
+import { BaseChatModel } from '@langchain/core/language_models/chat_models';
+
+let openrouterChatModels: Record<string, string>[] = [];
+
+async function fetchModelList(): Promise<void> {
+  try {
+    const response = await fetch('https://openrouter.ai/api/v1/models', {
+      method: 'GET',
+      headers: {
+        'Content-Type': 'application/json',
+      },
+    });
+
+    if (!response.ok) {
+      throw new Error(`API request failed with status: ${response.status}`);
+    }
+
+    const data = await response.json();
+
+    openrouterChatModels = data.data.map((model: any) => ({
+      displayName: model.name,
+      key: model.id,
+    }));
+  } catch (error) {
+    console.error('Error fetching models:', error);
+  }
+}
+
+export const loadOpenrouterChatModels = async () => {
+  await fetchModelList();
+
+  const openrouterApikey = getOpenrouterApiKey();
+
+  if (!openrouterApikey) return {};
+
+  try {
+    const chatModels: Record<string, ChatModel> = {};
+
+    openrouterChatModels.forEach((model) => {
+      chatModels[model.key] = {
+        displayName: model.displayName,
+        model: new ChatOpenAI({
+          openAIApiKey: openrouterApikey,
+          modelName: model.key,
+          temperature: 0.7,
+          configuration: {
+            baseURL: 'https://openrouter.ai/api/v1',
+          },
+        }) as unknown as BaseChatModel,
+      };
+    });
+
+    return chatModels;
+  } catch (err) {
+    console.error(`Error loading Openrouter models: ${err}`);
+    return {};
+  }
+};