feat(readarr): fetch the Readarr system status and expose it on the CLI

Add ReadarrEvent::GetStatus, mapped to GET /system/status, and
get_readarr_status in the new readarr_network/system module. It stores
the version and start time on ReadarrData so the system view and the
tick refresh can read them.

Surface it as `managarr readarr get system-status`, matching the
Radarr, Sonarr, and Lidarr spelling of the same call. A `list status`
spelling would have made the same command a different verb on the
fourth servarr, which is a difference the user would have to remember
for no benefit.

Readarr instances answer /system/status with thirty keys; SystemStatus
models the two that are used and serde ignores the rest, as it does for
the other three servarrs.

This is the first ReadarrCommand variant, so ReadarrCliHandler now
reads its app and network fields.

src/cli/readarr/get_command_handler.rs

@@ -0,0 +1,63 @@
+use std::sync::Arc;
+
+use anyhow::Result;
+use clap::Subcommand;
+use tokio::sync::Mutex;
+
+use crate::{
+  app::App,
+  cli::{CliCommandHandler, Command},
+  network::{NetworkTrait, readarr_network::ReadarrEvent},
+};
+
+use super::ReadarrCommand;
+
+#[cfg(test)]
+#[path = "get_command_handler_tests.rs"]
+mod get_command_handler_tests;
+
+#[derive(Debug, Clone, PartialEq, Eq, Subcommand)]
+pub enum ReadarrGetCommand {
+  #[command(about = "Get the system status")]
+  SystemStatus,
+}
+
+impl From<ReadarrGetCommand> for Command {
+  fn from(value: ReadarrGetCommand) -> Self {
+    Command::Readarr(ReadarrCommand::Get(value))
+  }
+}
+
+pub(super) struct ReadarrGetCommandHandler<'a, 'b> {
+  _app: &'a Arc<Mutex<App<'b>>>,
+  command: ReadarrGetCommand,
+  network: &'a mut dyn NetworkTrait,
+}
+
+impl<'a, 'b> CliCommandHandler<'a, 'b, ReadarrGetCommand> for ReadarrGetCommandHandler<'a, 'b> {
+  fn with(
+    _app: &'a Arc<Mutex<App<'b>>>,
+    command: ReadarrGetCommand,
+    network: &'a mut dyn NetworkTrait,
+  ) -> Self {
+    ReadarrGetCommandHandler {
+      _app,
+      command,
+      network,
+    }
+  }
+
+  async fn handle(self) -> Result<String> {
+    let result = match self.command {
+      ReadarrGetCommand::SystemStatus => {
+        let resp = self
+          .network
+          .handle_network_event(ReadarrEvent::GetStatus.into())
+          .await?;
+        serde_json::to_string_pretty(&resp)?
+      }
+    };
+
+    Ok(result)
+  }
+}