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/api-types/src/responses.rs

@@ -83,6 +83,13 @@ pub struct TopFriendsResponse {
     pub top_friends: Vec<UserResponse>,
 }
 
+#[derive(Serialize, utoipa::ToSchema)]
+#[serde(rename_all = "camelCase")]
+pub struct NotificationSummaryResponse {
+    pub total: i64,
+    pub unread: u64,
+}
+
 #[derive(Serialize, utoipa::ToSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct ErrorResponse {