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/domain/src/ports.rs

@@ -188,9 +188,17 @@ pub trait UserRepository: Send + Sync {
         user_id: &UserId,
         bio: Option<String>,
         avatar_path: Option<String>,
+        banner_path: Option<String>,
+        also_known_as: Option<String>,
     ) -> Result<(), DomainError>;
 }
 
+#[async_trait]
+pub trait UserProfileFieldsRepository: Send + Sync {
+    async fn get_fields(&self, user_id: &UserId) -> Result<Vec<crate::models::ProfileField>, DomainError>;
+    async fn set_fields(&self, user_id: &UserId, fields: Vec<crate::models::ProfileField>) -> Result<(), DomainError>;
+}
+
 #[async_trait]
 pub trait EventPublisher: Send + Sync {
     async fn publish(&self, event: &DomainEvent) -> Result<(), DomainError>;