fix: normalize Ollama URLs to handle trailing slashes

[roomote]

This PR fixes issue #6078 where trailing slashes in Ollama API URLs were causing 405 errors and misleading error messages about models not supporting embeddings.

Problem

When users configure their Ollama base URL with a trailing slash (e.g., http://localhost:11434/), the URL concatenation in the code would create double slashes (e.g., http://localhost:11434//api/embed), leading to API call failures.

Solution

• Created a new url-normalization utility that removes trailing slashes from base URLs
• Added a joinUrlPath function to safely join base URLs with paths
• Updated all Ollama-related code to use these utilities:
  • src/api/providers/ollama.ts
  • src/services/code-index/embedders/ollama.ts
  • src/api/providers/fetchers/ollama.ts

Testing

• Added comprehensive unit tests for the URL normalization utility
• All existing tests pass without regression
• The fix ensures that URLs are properly normalized regardless of whether users include trailing slashes

This change improves the user experience by preventing confusing errors when configuring Ollama endpoints.

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Important

Fixes issue #6078 by normalizing Ollama API URLs to handle trailing slashes, preventing 405 errors.

• Behavior:
  • Fixes issue Ollama URL normalization (leading to issues like #5007) does not clean trailing / #6078 by normalizing Ollama API URLs to prevent 405 errors due to trailing slashes.
  • Introduces normalizeBaseUrl and joinUrlPath in url-normalization.ts to handle URL concatenation.
  • Updates URL handling in src/api/providers/ollama.ts, src/api/providers/fetchers/ollama.ts, and src/services/code-index/embedders/ollama.ts to use new utilities.
• Testing:
  • Adds unit tests in url-normalization.test.ts to verify URL normalization and joining behavior.
  • Ensures all existing tests pass without regression.

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[Naam]

So that's essentially a duplicate of the one I proposed in #6079 ?