Fix warnings: remove unused import and variable

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

warzone/crates/warzone-client/src/main.rs

@@ -123,7 +123,6 @@ async fn main() -> anyhow::Result<()> {
             tui::run_tui(our_fp, peer, server, identity, poll_seed, db).await?;
         }
         Commands::Backup { output } => {
-            let data_dir = keystore::data_dir();
             // Collect all sled data as JSON
             let db = storage::LocalDb::open()?;
             let backup_data = db.export_all()?;