fix(upgrade): Use GitHub release as latest version

Use GitHub releases as the canonical source for upgrade checks so stale
package-manager metadata cannot report an old version as latest.

Preserve the exact release tag when fetching release notes so multi-version
upgrades show notes for the actual target release.

Co-Authored-By: Codex <noreply@openai.com>

Author: cameroncooke

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## [Unreleased]
+
+### Fixed
+
+- Fixed `xcodebuildmcp upgrade` so update checks use the latest GitHub release as the canonical target instead of stale package-manager metadata, ensuring multi-version upgrades show release notes for the actual target version.
+
 ## [2.6.1]
 
 ### Fixed