Add --dry-run support for --update to check for updates without installing

[ryanfowler]

No description provided.

[Copilot]

Pull request overview

This PR adds --dry-run support for the --update flag, allowing users to check for available updates without installing them.

Changes:

• Added dryRun parameter to update-related functions to propagate the dry-run flag through the update flow
• Implemented dry-run logic to display update availability without performing the actual update
• Added integration tests to verify dry-run behavior when already on latest version and when updates are available
• Updated CLI documentation to describe the new --dry-run behavior with --update

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
main.go	Passes the app.DryRun flag to the update.Update function
internal/update/update.go	Adds dryRun parameter to update functions and implements early return logic when dry-run is enabled
integration/integration_test.go	Adds test cases to verify dry-run update behavior for both same version and available update scenarios
docs/cli-reference.md	Updates documentation for --update and --dry-run flags to describe the new combined behavior

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