feat(readarr): fetch Readarr authors and expose them on the CLI

Add ReadarrEvent::ListAuthors, mapping to GET /author, and wire it up as
`managarr readarr list authors`.

This is the first Readarr event that touches the library rather than
configuration, so it creates the library/authors module tree mirroring
Lidarr's library/artists layout.

list_authors mirrors Lidarr's list_artists, including the sort-prompt
route guard: a response landing while the user has the sort prompt open
must not clobber their in-progress sort selection. Both directions of
that guard are covered by tests.

src/network/readarr_network/mod.rs

@@ -7,6 +7,7 @@ use crate::models::readarr_models::{AddReadarrRootFolderBody, ReadarrSerdeable,
 use crate::models::servarr_models::{MetadataProfile, QualityProfile, Tag};
 use crate::network::{Network, RequestMethod};
 
+mod library;
 mod root_folders;
 mod system;
 
@@ -33,12 +34,14 @@ pub enum ReadarrEvent {
   GetTasks,
   GetUpdates,
   HealthCheck,
+  ListAuthors,
   StartTask(ReadarrTaskName),
 }
 
 impl NetworkResource for ReadarrEvent {
   fn resource(&self) -> &'static str {
     match &self {
+      ReadarrEvent::ListAuthors => "/author",
       ReadarrEvent::GetQueuedEvents | ReadarrEvent::StartTask(_) => "/command",
       ReadarrEvent::GetHostConfig | ReadarrEvent::GetSecurityConfig => "/config/host",
       ReadarrEvent::GetDiskSpace => "/diskspace",
@@ -122,6 +125,7 @@ impl Network<'_, '_> {
         .get_readarr_healthcheck()
         .await
         .map(ReadarrSerdeable::from),
+      ReadarrEvent::ListAuthors => self.list_authors().await.map(ReadarrSerdeable::from),
       ReadarrEvent::StartTask(task_name) => self
         .start_readarr_task(task_name)
         .await