refactor: type safety + dedup cleanup across 13 code smells

- typed PagedResponse/CreatedApiKeyResponse/NotificationSummaryResponse replace json! blocks
- extract TagRow/ApiKeyRow/OutboxRow to module level, top_friend uses sqlx flatten
- add should_broadcast() helper, inline dead let bindings in federation_event
- add UploadContext struct, extract_upload_field, wants_activity_json helpers
- rename PostgresFederationRepository→PgFederationRepository, PostgresApUserRepository→PgApUserRepository
- add IntoAnyhow trait replacing ~30 .map_err(|e| anyhow!(e)) calls
- extract build_ap_service shared between bootstrap and worker factories
- add postgres/constants.rs, PartialEq+Eq on PasswordHash

crates/domain/src/value_objects/mod.rs

@@ -89,7 +89,7 @@ impl Email {
     }
 }
 
-#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
 pub struct PasswordHash(pub String);
 
 #[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]