fix: index the standalone layout for regions

GC/EUR/IPL.bin fell through to its bare name and the union of five regions, so a Batocera or standalone Dolphin pack never reduced it. The GameCube IPLs of four Dolphin-family profiles now name their system, as the MMJR profiles do.

scripts/slot.py

@@ -60,7 +60,8 @@ def build_slot_index(profiles: dict) -> dict[str, dict]:
                 continue
             name = f.get("name", "")
             path = f.get("path") or ""
-            for key in {path, name} - {""}:
+            # Keyed by the standalone layout too, as build_region_index is.
+            for key in {path, f.get("standalone_path") or "", name} - {""}:
                 entry = index.setdefault(
                     key,
                     {"rank": None, "conflict": False, "regions": set(),