Refactor hook registration and init order in ActivityPub

[obenland]

Proposed changes:

• Moved activation, deactivation, and uninstall hook registration to use class references directly.
• Consolidated and reordered 'init' actions in Activitypub::init() for better clarity and maintainability.
• Fixed import order in class-activitypub.php and ensured Embed::init() is called via an 'init' action in activitypub.php.

[Copilot]

Pull Request Overview

This PR refactors the ActivityPub plugin initialization by consolidating hook registrations and improving code organization. The changes focus on moving lifecycle hooks to use class references directly and reordering initialization actions for better maintainability.

• Moved activation, deactivation, and uninstall hook registrations to use class references directly
• Consolidated and reordered 'init' actions in Activitypub::init() method
• Fixed import order and ensured Embed::init() is called via an 'init' action

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
includes/class-activitypub.php	Reordered imports, consolidated init actions, and moved post type support registration
activitypub.php	Simplified hook registrations using class references and added Embed::init() to plugin_init()

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