Consolidate release url extraction

[cyanzhong]

No description provided.

[Copilot]

Pull request overview

This pull request updates ExtensionRelease.pageURL extraction to handle raw.githubusercontent.com/.../refs/tags/... URL shapes, and extends unit coverage to ensure both “official” and non-official repositories produce the expected GitHub page URLs.

Changes:

• Extend ExtensionRelease.pageURL parsing to treat raw.githubusercontent.com/{owner}/{repo}/refs/tags/{tag}/... as {ref} = {tag}.
• Add new unit tests for raw tag-ref URLs for both generic and MarkEdit-app repositories.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
MarkEditMac/Modules/Tests/ExtensionCoreTests.swift	Adds test coverage for raw.githubusercontent.com/.../refs/tags/... page URL derivation, including official repo behavior.
MarkEditMac/Modules/Sources/ExtensionCore/ExtensionRegistry.swift	Updates pageURL extraction to correctly pull the tag name from refs/tags raw URLs.

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