fix: validate location URLs using URL constructor in CalEventParser

[NikolaVujovic1988]

Summary

• Replaces regex-based URL check (/^https?:\/\//) with proper URL constructor validation in getProviderName
• Removes the stale TODO comment — packages/lib must not import from @calcom/app-store per architecture rules

Context

Addresses review feedback from #28242, where @romitg2 requested using an existing library/function for URL validation rather than simply removing the comment.

The URL constructor is already used for validation elsewhere in packages/lib (e.g., getSafeRedirectUrl.ts) and requires no additional dependencies.

Test plan

• No functional changes — URL validation behavior is preserved with stricter parsing
• yarn type-check:ci --force passes

[cubic-dev-ai]

No issues found across 1 file