fix: normalize OpenAI custom base URLs with or without /v1 suffix

[roomote]

This PR attempts to address Issue #9426. Feedback and guidance are welcome.

Problem

Users were encountering errors when using custom OpenAI-compatible base URLs:

• URLs with /v1 suffix would error
• URLs without /v1 suffix would also error
• The OpenAI provider was not properly handling custom base URLs

Solution

• Added a normalizeOpenAiBaseUrl helper function to intelligently handle URL normalization
• Automatically appends /v1 suffix to OpenAI-compatible URLs when missing
• Properly detects and skips normalization for Azure endpoints which use different path structures
• Applied normalization to both OpenAiHandler constructor and getOpenAiModels function

Changes

• Modified src/api/providers/openai.ts to add URL normalization logic
• Added comprehensive test coverage in src/api/providers/__tests__/openai.spec.ts

Testing

• Added unit tests for various URL formats (with/without /v1, trailing slashes, Azure endpoints)
• All existing tests pass without regression
• New tests verify proper URL normalization behavior

Fixes #9426

---

Important

Adds URL normalization for OpenAI-compatible base URLs, ensuring consistent handling with or without '/v1' suffix, excluding Azure endpoints.

• Behavior:
  • Adds normalizeOpenAiBaseUrl function to handle URL normalization in openai.ts.
  • Automatically appends /v1 to OpenAI-compatible URLs if missing, except for Azure endpoints.
  • Applies normalization in OpenAiHandler constructor and getOpenAiModels function.
• Testing:
  • Adds unit tests in openai.spec.ts for URL formats with/without /v1, trailing slashes, and Azure endpoints.
  • Ensures all existing tests pass without regression.
• Misc:
  • Updates openai.ts to use normalizeOpenAiBaseUrl in URL handling logic.

^{This description was created by for 4cb6444. You can customize this summary. It will automatically update as commits are pushed.}

[roomote]

Rooviewer   See task on Roo Cloud

Review completed. The implementation successfully addresses the custom OpenAI base URL issue with proper URL normalization, comprehensive test coverage, and correct handling of Azure endpoints. No issues found.

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}