feat(readarr): fetch Readarr disk space and expose it on the CLI

Add ReadarrEvent::GetDiskSpace, mapped to GET /diskspace, and
get_readarr_diskspace, which stores the result on ReadarrData for the
root folder and system views.

Surface it as `managarr readarr list disk-space`, matching the other
three servarrs.

Readarr returns a label field on some records that DiskSpace does not
model; serde drops it, so the CLI prints only the path and the free and
total space, as it does for the other three servarrs.

src/cli/readarr/list_command_handler_tests.rs

@@ -0,0 +1,73 @@
+#[cfg(test)]
+mod tests {
+  use crate::Cli;
+  use crate::cli::{
+    Command,
+    readarr::{ReadarrCommand, list_command_handler::ReadarrListCommand},
+  };
+  use clap::CommandFactory;
+  use pretty_assertions::assert_eq;
+
+  #[test]
+  fn test_readarr_list_command_from() {
+    let command = ReadarrListCommand::DiskSpace;
+
+    let result = Command::from(command.clone());
+
+    assert_eq!(result, Command::Readarr(ReadarrCommand::List(command)));
+  }
+
+  mod cli {
+    use rstest::rstest;
+
+    use super::*;
+
+    #[rstest]
+    fn test_list_commands_have_no_arg_requirements(#[values("disk-space")] subcommand: &str) {
+      let result = Cli::command().try_get_matches_from(["managarr", "readarr", "list", subcommand]);
+
+      assert_ok!(&result);
+    }
+  }
+
+  mod handler {
+    use std::sync::Arc;
+
+    use mockall::predicate::eq;
+    use serde_json::json;
+    use tokio::sync::Mutex;
+
+    use crate::{
+      app::App,
+      cli::{
+        CliCommandHandler,
+        readarr::list_command_handler::{ReadarrListCommand, ReadarrListCommandHandler},
+      },
+      models::{Serdeable, readarr_models::ReadarrSerdeable},
+      network::{MockNetworkTrait, NetworkEvent, readarr_network::ReadarrEvent},
+    };
+
+    #[tokio::test]
+    async fn test_handle_list_disk_space_command() {
+      let mut mock_network = MockNetworkTrait::new();
+      mock_network
+        .expect_handle_network_event()
+        .with(eq::<NetworkEvent>(ReadarrEvent::GetDiskSpace.into()))
+        .times(1)
+        .returning(|_| {
+          Ok(Serdeable::Readarr(ReadarrSerdeable::Value(
+            json!({"testResponse": "response"}),
+          )))
+        });
+      let app_arc = Arc::new(Mutex::new(App::test_default()));
+      let list_disk_space_command = ReadarrListCommand::DiskSpace;
+
+      let result =
+        ReadarrListCommandHandler::with(&app_arc, list_disk_space_command, &mut mock_network)
+          .handle()
+          .await;
+
+      assert_ok!(&result);
+    }
+  }
+}