feat(readarr): trigger automatic author searches and expose the command on the CLI

Posts the AuthorSearch command to the command endpoint with the author ID, queueing an indexer search for that author. The response is returned verbatim and no app state is mutated.

Introduces ReadarrCommandBody, the request body shared by the author and book command calls. Both ID fields are omitted from the payload when absent rather than sent as null.

src/models/readarr_models.rs

@@ -220,6 +220,16 @@ pub struct AddAuthorSearchResult {
   pub ratings: Option<Ratings>,
 }
 
+#[derive(Default, Serialize, Debug)]
+#[serde(rename_all = "camelCase")]
+pub struct ReadarrCommandBody {
+  pub name: String,
+  #[serde(skip_serializing_if = "Option::is_none")]
+  pub author_id: Option<i64>,
+  #[serde(skip_serializing_if = "Option::is_none")]
+  pub book_ids: Option<Vec<i64>>,
+}
+
 #[derive(Serialize, Deserialize, Debug, Default, Clone, Eq, PartialEq)]
 #[serde(rename_all = "lowercase")]
 pub struct DeleteParams {