Filter out Max Raid den routes from Sword/Shield game data

Den child routes (~561 per game) bloated the route list without being
useful for Nuzlocke tracking. Adds filter_den_routes() to strip children
matching "(Den " from the route hierarchy, reducing Sw/Sh from ~1,007
to 446 routes each.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tools/import-pokedb/import_pokedb/processing.py

@@ -341,3 +341,15 @@ def build_routes(
                 ))
 
     return routes
+
+
+def filter_den_routes(routes: list[Route]) -> list[Route]:
+    """Remove Max Raid den child routes from the route list.
+
+    Dens are identified by "(Den " in the child route name.
+    Only children are filtered — parent routes are kept.
+    """
+    for route in routes:
+        if route.children:
+            route.children = [c for c in route.children if "(Den " not in c.name]
+    return routes