feat(llm): add API format selector to custom provider for OpenAI compatibility

[h0ll0w-AkuZr0guY]

Description

This PR addresses the issue where using an OpenAI-compatible endpoint (like free.v36.cm or local proxies) in the Custom provider results in a 404 error. The error occurs because the application previously defaulted all custom endpoints to Anthropic's /v1/messages format, whereas OpenAI-compatible APIs expect /v1/chat/completions.

Instead of using implicit URL pattern detection, I implemented a more reliable explicit approach: adding an API Format selector (Anthropic Standard vs. OpenAI Compatible) under the Custom provider settings. This routes requests through the newly implemented openai-adapter.ts when needed, ensuring perfect compatibility without breaking existing custom Anthropic endpoints.

Fixes #12

Key Changes

• Settings UI: Added an API Format dropdown in GeneralSettings.tsx when the Custom provider is selected.
• Config & Types: Updated shared.tsx, preload/index.d.ts, and settings.config.ts to include the customFormat state ('anthropic' | 'openai').
• Client Factory: Modified createClient in utils.ts to return an OpenAI client instance if the user selects the openai format.
• Agent Routing: Expanded the adapter condition in agent.service.ts (runAgentLoop and evaluate) to route custom + openai format requests through the runOpenAIAdapter.

Testing Instructions

1. Navigate to Settings > General, select Custom Provider.

2. Change the API Format to OpenAI Compatible.

3. Input an OpenAI-compatible proxy URL (e.g., http://localhost:11434/v1) and API Key.

4. Test a conversation to verify successful communication via /v1/chat/completions.

Screenshots

Checklist

• Followed TypeScript best practices and added type annotations
• Tested changes locally (npm run dev:memu)