refactor: 5 architectural improvements (Tasks 2-5 + Task 6 fix)

- feat(domain): Hashtag value object with canonical extract() — unifies two
  divergent private implementations; fields pre-compute raw/normalized/url_slug/ap_name

- feat(presentation): Deps<S: FromAppState> extractor — each handler now
  declares its exact dependency surface; AppState unchanged; handlers
  become unit-testable without mocking all 20 deps

- refactor(feed): replace 5 flat FeedRepository methods with FeedQuery/FeedScope
  — single query() method; SQL shared logic lives once; adding feed types
  no longer requires 5 edits

- refactor(activitypub): ActivityPubRepository + OutboundFederationPort moved
  out of domain::ports into activitypub-base::ap_ports — domain crate no
  longer knows about AP IDs, inboxes, or actor URLs

- fix(outbox): OutboxRelay now opens a per-row transaction so FOR UPDATE
  SKIP LOCKED actually holds the lock during publish + mark_delivered

crates/adapters/postgres/Cargo.toml

@@ -4,9 +4,10 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-domain        = { workspace = true }
-event-payload = { workspace = true }
-sqlx          = { workspace = true }
+domain           = { workspace = true }
+activitypub-base = { workspace = true }
+event-payload    = { workspace = true }
+sqlx             = { workspace = true }
 uuid        = { workspace = true }
 serde_json  = { workspace = true }
 chrono      = { workspace = true }