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.rs

@@ -0,0 +1,62 @@
+use std::sync::Arc;
+
+use anyhow::Result;
+use clap::Subcommand;
+use tokio::sync::Mutex;
+
+use super::ReadarrCommand;
+use crate::{
+  app::App,
+  cli::{CliCommandHandler, Command},
+  network::{NetworkTrait, readarr_network::ReadarrEvent},
+};
+
+#[cfg(test)]
+#[path = "list_command_handler_tests.rs"]
+mod list_command_handler_tests;
+
+#[derive(Debug, Clone, PartialEq, Eq, Subcommand)]
+pub enum ReadarrListCommand {
+  #[command(about = "List disk space details for all provisioned root folders in Readarr")]
+  DiskSpace,
+}
+
+impl From<ReadarrListCommand> for Command {
+  fn from(value: ReadarrListCommand) -> Self {
+    Command::Readarr(ReadarrCommand::List(value))
+  }
+}
+
+pub(super) struct ReadarrListCommandHandler<'a, 'b> {
+  _app: &'a Arc<Mutex<App<'b>>>,
+  command: ReadarrListCommand,
+  network: &'a mut dyn NetworkTrait,
+}
+
+impl<'a, 'b> CliCommandHandler<'a, 'b, ReadarrListCommand> for ReadarrListCommandHandler<'a, 'b> {
+  fn with(
+    _app: &'a Arc<Mutex<App<'b>>>,
+    command: ReadarrListCommand,
+    network: &'a mut dyn NetworkTrait,
+  ) -> Self {
+    ReadarrListCommandHandler {
+      _app,
+      command,
+      network,
+    }
+  }
+
+  async fn handle(self) -> Result<String> {
+    let result = match self.command {
+      ReadarrListCommand::DiskSpace => {
+        let resp = self
+          .network
+          .handle_network_event(ReadarrEvent::GetDiskSpace.into())
+          .await?;
+        serde_json::to_string_pretty(&resp)?
+      }
+    };
+
+    Ok(result)
+  }
+}