feat: support sync OpenAI models

[Louis-7]

Pull Request Template

Description

Support sync OpenAI models to the app.

Related Issue

#11

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor
• Other

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[Copilot]

Pull Request Overview

This PR refactors the OpenAI provider to properly handle custom API endpoints and improve URL construction. The changes standardize the host configuration to use a base URL (/v1) instead of full endpoint paths, introduce helper methods for URL construction, and add API model syncing support.

Key changes:

• Introduced URL parsing logic to derive base API URL and construct endpoint-specific URLs
• Changed default host configuration from full endpoint path to base URL
• Added constants for API paths and default origin
• Removed fallback return in error handling for listModels() method

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/services/providers/OpenAIProvider.ts	Refactored URL construction with new helper methods, added constants, typed API response, removed error fallback
src/pages/Settings/Models/ProviderOpenAI.tsx	Updated placeholder to reflect new base URL format, enabled sync button for model fetching
settings.default.json	Changed default host from full endpoint path to base URL