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

Cargo.lock

@@ -1368,7 +1368,7 @@ dependencies = [
 
 [[package]]
 name = "k-ap"
-version = "0.1.9"
+version = "0.2.0"
 dependencies = [
  "activitypub_federation",
  "anyhow",
@@ -1384,6 +1384,7 @@ dependencies = [
  "tracing",
  "url",
  "uuid",
+ "zeroize",
 ]
 
 [[package]]
@@ -3230,6 +3231,20 @@ name = "zeroize"
 version = "1.8.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b97154e67e32c85465826e8bcc1c59429aaaf107c1e4a9e53c8d8ccd5eff88d0"
+dependencies = [
+ "zeroize_derive",
+]
+
+[[package]]
+name = "zeroize_derive"
+version = "1.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85a5b4158499876c763cb03bc4e49185d3cccbabb15b33c627f7884f43db852e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.117",
+]
 
 [[package]]
 name = "zerotrie"