feat: add normalized config tracking and improve command

- Add normalize_to_final_build() to map tune configs to final builds (323/233/332)
- Add normalized_config field to BestCarRecord
- Change CarCounts.by_rid key from String to (String, String) for per-config tracking
- Change CarCounts.guid_to_rid to HashMap<String, HashSet<(String, String)>>
- Extract owned tune configs from my_cars.json (engineMajor/weightMajor/chassisMajor)
- Add improve command: owned cars not yet at final build, sorted by track count
- Strip version prefixes (v2c_/v1c_) from config keys at parse time
- Update dedup check in update_best_car to consider normalized_config
- Add atomic_write helper for safe CSV output
- Delete completed plans/code-review-v2.md
- Apply rustfmt formatting across codebase

src/commands/improve.rs

@@ -0,0 +1,27 @@
+//! Improve command implementation.
+//!
+//! Generates improve.csv — owned cars not yet in a final configuration,
+//! sorted by number of best tracks (descending).
+
+use top_drives::AppError;
+
+use crate::commands::{load_my_cars_or_warn, run_analysis};
+use crate::output::write_improve_csv;
+
+/// Executes the improve command: generates improve.csv.
+pub async fn run_improve(
+    my_cars_path: &str,
+    cars_db_path: &str,
+    times_dir: &str,
+    output_dir: &str,
+) -> Result<(), AppError> {
+    let my_data = load_my_cars_or_warn(my_cars_path)?;
+    let (_ctx, counts) = run_analysis(&my_data, cars_db_path, times_dir).await?;
+    let count = write_improve_csv(output_dir, &counts)?;
+    if count == 0 {
+        println!("No cars to improve — all owned cars are already in final or maxed configs.");
+    } else {
+        println!("Written: improve.csv ({count} cars to improve)");
+    }
+    Ok(())
+}