Actor deletion with an admin-chosen object policy

[2chanhaeng]

• Add local_instances.actor_deletion_policy (delete, anonymize, preserve) and activities.deleted, with a migration.
• Add deleteActor for instance admins, applying the policy to its objects and activities in one transaction (anonymize scrubs the profile, preserve keeps them served).
• Add a policy setter.
• Federated Delete follows Store actor key pairs and register the key pairs dispatcher #87.

Tracks the FIXME at actors.deleted in packages/models/src/schema.ts.

AI disclosure

The user asked Claude Code (claude-fable-5-1) to survey every FIXME comment in the codebase and draft an issue for each. The user read and edited the drafts, then directed Claude Code to file them through the GitHub CLI.