feat: production hardening — security, scale, protocol, DX

Breaking changes to FederationRepository, ApObjectHandler, ApUser:

FederationRepository:
- add is_activity_processed / mark_activity_processed (inbox idempotency)
- add get_accepted_follower_inboxes (DB-side dedup/filtering, replaces in-memory load-all)

ApObjectHandler:
- add on_announce_of_remote (cross-server boosts, previously silently dropped)

ApUser:
- add manually_approves_followers: bool
- add actor_type: ApActorType (was hardcoded Person)

Security:
- block check before actor HTTP fetch in Follow (prevents SSRF on blocked actors)
- 4xx responses use generic "not found"/"bad request" (no internal leak)
- 1 MB DefaultBodyLimit on inbox routes
- zeroize private key after generation

Delivery:
- all broadcasts are now non-blocking (tokio::spawn fallback, or EventPublisher queue)
- EventPublisher redesigned with typed FederationEvent enum (DeliveryRequested/DeliveryFailed)
- new deliver_to_inbox() public method for queue consumers
- configurable delivery_max_attempts and delivery_initial_delay_secs via builder
- Follow saved as Pending BEFORE delivery (race condition fix)

Router:
- GET /users/{id} (actor), GET /users/{id}/followers, GET /users/{id}/following now mounted

Protocol:
- mention extraction from Create/Update tag arrays → on_mention() dispatched
- WebFinger: add aliases field (acct: URI + AP actor URL)
- outbox: add last link, use count_local_posts for totalItems
- idempotency guard added to every inbound activity receive()
- actor serializes display_name and configurable actor_type/manually_approves_followers

Bump: 0.1.10 → 0.2.0

src/tests/actors.rs

@@ -10,9 +10,9 @@ fn person_serializes_with_enriched_fields() {
             .into(),
         preferred_username: "alice".to_string(),
         inbox: "https://example.com/users/1/inbox".parse().unwrap(),
-        outbox: "https://example.com/users/1/outbox".parse().unwrap(),
-        followers: "https://example.com/users/1/followers".parse().unwrap(),
-        following: "https://example.com/users/1/following".parse().unwrap(),
+        outbox: Some("https://example.com/users/1/outbox".parse().unwrap()),
+        followers: Some("https://example.com/users/1/followers".parse().unwrap()),
+        following: Some("https://example.com/users/1/following".parse().unwrap()),
         public_key: PublicKey {
             id: "https://example.com/users/1#main-key".to_string(),
             owner: "https://example.com/users/1".parse().unwrap(),