Tighter A* estimate on the orthogonal track, and --heuristic-weight

The grid search estimated the remaining distance as a straight line even
when only orthogonal steps exist; Manhattan is the tighter estimate those
moves admit and still never overestimates. --heuristic-weight W (default
1) makes it weighted A*: routes at most W times the shortest (tested).

src/freeroute/cli.py

@@ -118,6 +118,14 @@ def build_parser() -> argparse.ArgumentParser:
         help="grid and exact engines: cells K times finer than trace + clearance "
         "(default 1); 2 or more reaches fine-pitch pins, at some cost in time",
     )
+    parser.add_argument(
+        "--heuristic-weight",
+        type=float,
+        default=1.0,
+        metavar="W",
+        help="exact engine: weighted A* (W >= 1); larger is faster, routes at most "
+        "W times the shortest length (default 1)",
+    )
     parser.add_argument(
         "--edge-clearance",
         type=float,
@@ -175,6 +183,7 @@ def main(argv: list[str] | None = None) -> int:
             max_passes=max_passes,
             edge_clearance_mm=args.edge_clearance,
             resolution=args.grid_resolution,
+            heuristic_weight=args.heuristic_weight,
         )
     elif args.engine == "room":
         result = build_rooms_routing_result(