feat(ap): ActivityPub spec compliance and profile completeness

Phase 1 — spec compliance:
- Add AS_PUBLIC constant; add to/cc fields to CreateActivity, DeleteActivity,
  UpdateActivity, AddActivity; populate on all broadcast call sites
- Add @context to outbox CreateActivity items
- Set manuallyApprovesFollowers: true to match actual Pending follow flow
- Gate PermissiveVerifier behind FEDERATION_DEBUG env var
- Add updated timestamp to Person actor JSON
- Improve actor update delivery logging

Phase 2a Batch 1 — AP layer:
- Add /inbox shared inbox route; add endpoints.sharedInbox to Person
- Paginate followers and following collections (20/page, OrderedCollectionPage)

Phase 2a Batch 2 — profile completeness:
- DB migrations: banner_path, also_known_as columns; user_profile_fields table
- ProfileField value object; UserProfileFieldsRepository port
- Banner image upload (stored via image-converter, surfaced as image in Person)
- alsoKnownAs field in Person (account migration support)
- Custom profile fields (up to 4 PropertyValue attachments in Person)
- Profile settings UI: banner preview/upload, alsoKnownAs input, fields form
- PUT /api/v1/profile/fields API endpoint

crates/application/src/commands.rs

@@ -78,6 +78,14 @@ pub struct UpdateProfileCommand {
     pub bio: Option<String>,
     pub avatar_bytes: Option<Vec<u8>>,
     pub avatar_content_type: Option<String>,
+    pub banner_bytes: Option<Vec<u8>>,
+    pub banner_content_type: Option<String>,
+    pub also_known_as: Option<String>,
+}
+
+pub struct UpdateProfileFieldsCommand {
+    pub user_id: Uuid,
+    pub fields: Vec<domain::models::ProfileField>,
 }
 
 pub struct EnrichMovieCommand {