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/types.rs

@@ -74,8 +74,12 @@ pub struct BestCarRecord {
     pub year: u16,
     /// Rarity level of this specific car configuration
     pub rq: u8,
-    /// Tune configuration string (e.g., "111", "233", "323")
+    /// Original tune configuration string from JSON (e.g., "111", "221", "233")
     pub config: String,
+    /// Normalized config mapped to the closest final build ("323", "233", or "332").
+    /// Final builds are permutations of digits summing to 8. Non-standard configs
+    /// are normalized by repeatedly incrementing the smallest digit until the sum is 8.
+    pub normalized_config: String,
     /// Track time in seconds (lower is better)
     pub time: f64,
     /// Whether the current user owns this car
@@ -89,3 +93,59 @@ pub struct BestCarRecord {
 /// Type alias for the composite key used to identify unique track conditions.
 /// Consists of: (Track ID, RQ Level, Surface Condition)
 pub type TripletKey = (String, u8, String);
+
+/// Normalizes a tune configuration to the closest "final build".
+///
+/// The three final builds are "323", "233", and "332" (all permutations of digits
+/// summing to 8). For any non-standard config, this function repeatedly increments
+/// the smallest digit until the digit sum reaches 8, producing one of the three
+/// final builds.
+///
+/// Expects bare digit strings (e.g., `"233"`, `"111"`). Version prefixes (e.g.,
+/// `"v2c_233"`) are stripped at read time by the parsing layer before reaching
+/// this function.
+///
+/// If the config cannot be parsed (wrong length, non-digit characters, or digit
+/// sum exceeding 8), the original config string is returned unchanged.
+///
+/// # Examples
+///
+/// ```
+/// use top_drives::normalize_to_final_build;
+/// assert_eq!(normalize_to_final_build("323"), "323");
+/// assert_eq!(normalize_to_final_build("111"), "332");
+/// assert_eq!(normalize_to_final_build("221"), "332");
+/// assert_eq!(normalize_to_final_build("122"), "332");
+/// assert_eq!(normalize_to_final_build("113"), "323");
+/// assert_eq!(normalize_to_final_build("233"), "233");
+/// assert_eq!(normalize_to_final_build("332"), "332");
+/// assert_eq!(normalize_to_final_build("879"), "879");  // maxed: returned as-is
+/// ```
+pub fn normalize_to_final_build(config: &str) -> String {
+    let bytes = config.as_bytes();
+    if bytes.len() != 3 || !bytes.iter().all(|&b| b.is_ascii_digit()) {
+        return config.to_string();
+    }
+
+    let mut digits = [0u8; 3];
+    for (i, &b) in bytes.iter().enumerate() {
+        digits[i] = b - b'0';
+    }
+
+    let sum: i32 = digits.iter().map(|&d| d as i32).sum();
+    if sum >= 8 {
+        // Already a final build (sum == 8) or maxed (sum > 8) — return as-is.
+        return config.to_string();
+    }
+
+    let mut deficit = 8 - sum;
+    while deficit > 0 {
+        // Find the position of the smallest digit (first occurrence on tie)
+        let min_pos = (0..3).min_by_key(|&i| digits[i]).unwrap();
+        digits[min_pos] += 1;
+        deficit -= 1;
+    }
+
+    digits.iter().map(|&d| (b'0' + d) as char).collect()
+}
+