Improve Compatibility with ActivityPub 7.0

[akirk]

• Use ActivityPub's follow() and unfollow() functions directly remove our custom queue-based actions
• Auto-create Friends subscriptions when following via ActivityPub plugin (via post_activitypub_add_to_outbox hook)
• Store ap_actor_id references instead of raw URLs in attributedTo metadata for better reliability
• New migration system with (bot yet linked) admin UI at ?page=friends-migrations:
• Registry-based migration architecture with batch support
• Migration to convert existing attributedTo URLs to ap_actor_id references
• New migration to link ActivityPub feeds to their corresponding ap_actor posts
• Edit feeds UI improvements: Show ActivityPub follow status and provide sync actions

[github-actions]

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