Fxing an issue removal of the registry path

[Shahafgo]

Greptile Summary

Fixed URL construction to preserve registry base paths when the registry is hosted at a non-root path (e.g., http://host/custom/registry/path). Previously, new URL('/api/v1/skills', 'http://host/base') would discard /base because absolute paths override the base URL's path component. The new registryUrl() helper normalizes both arguments to construct relative URLs, ensuring http://host/base/api/v1/skills.

• Introduced registryUrl() helper function in http.ts with proper path normalization
• Updated all URL construction sites across inspect.ts, moderation.ts, and skills.ts to use the new helper
• Added comprehensive test coverage in http.test.ts covering plain origins, custom base paths, trailing slashes, and encoded segments
• Fixed moderation.ts to pass complete URLs instead of pathname-only strings to maintain base path context

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The fix addresses a clear bug with proper encapsulation through a helper function, includes comprehensive test coverage for edge cases, and consistently applies the fix across all affected call sites. The implementation is straightforward with no complex logic or side effects.
• No files require special attention

_{Last reviewed commit: 8401d0d}

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[Shahafgo]

Attaching issue explanation: #433