Address review findings: const guards, qualifying-count regression test, owned keys

- Add compile-time const assertions (const _: () block, stable on 1.95)
  for MAX_RQ, MIN_VALID_TIME, TIME_TOLERANCE, TEST_BOWL_FACTOR, and
  CONCURRENCY_LIMIT so bad constant edits fail the build; remove the
  stale comment that incorrectly claimed compile-time validation existed
- Add regression test for the qualifying-count fix: car with 3 configs
  where only 2 meet min_count and 2 copies suffice to cover the
  qualifying ones (previously phantom-wishlisted via overcounting)
- Use owned String keys in qualifying_per_guid to decouple the map from
  guid_to_rid's allocations
- Clarify write_improve_csv doc (exactly one row per car), restore the
  remove.csv test section header, add trailing newline to .gitignore

src/parsing/mod.rs

@@ -46,6 +46,16 @@ pub const TEST_BOWL_FACTOR: f64 = 2000.0;
 /// since each concurrent permit holder also occupies a `spawn_blocking` thread.
 pub const CONCURRENCY_LIMIT: usize = 20;
 
+// Compile-time guards: a bad edit to any constant above fails the build here
+// instead of producing subtly wrong behavior at runtime.
+const _: () = {
+    assert!(MAX_RQ > 0);
+    assert!(MIN_VALID_TIME > 0.0);
+    assert!(TIME_TOLERANCE > 0.0);
+    assert!(TEST_BOWL_FACTOR > 0.0);
+    assert!(CONCURRENCY_LIMIT > 0);
+};
+
 // ---------------------------------------------------------------------------
 // Core parsing: per-car timing data
 // ---------------------------------------------------------------------------
@@ -736,10 +746,4 @@ mod tests {
             ctx.best_cars.get(&("Monaco Streets".to_string(), 90, "Wet".to_string())).unwrap();
         assert_eq!(records[0].config, "323", "bare config should pass through");
     }
-
-    // =======================================================================
-    // Constants tests
-    // =======================================================================
-    // Constants are compile-time validated - explicit tests removed as they
-    // check literal values that cannot fail unless the constants themselves are edited
 }