sorter: drop non-warhammer game systems (default: Middle-Earth)

The collection is warhammer-only; everything else stays in _unsorted
even when names match the catalog. The catalog snapshot keeps all
systems - the filter is a sorter default (DROPPED_SYSTEMS, applied in
load_catalog and after keyword classification), adjustable with
--drop-system/--keep-system.

sorter.py

@@ -27,6 +27,7 @@ import sys
 from pathlib import Path
 
 from dlphelper.sorter import (
+    DROPPED_SYSTEMS,
     format_plan,
     load_catalog,
     sort_plan,
@@ -57,8 +58,20 @@ def main() -> None:
                              "sort whole extraction directories as units")
     parser.add_argument("--json", action="store_true",
                         help="print the plan as JSON instead of text")
+    parser.add_argument("--drop-system", action="append", default=[],
+                        metavar="NAME",
+                        help="never place into this game system "
+                             "(default-dropped: Middle-Earth)")
+    parser.add_argument("--keep-system", action="append", default=[],
+                        metavar="NAME",
+                        help="re-enable a default-dropped game system")
     args = parser.parse_args()
 
+    dropped = frozenset(DROPPED_SYSTEMS - set(args.keep_system)
+                        | set(args.drop_system))
+    if args.keep_system or args.drop_system:
+        log.info("System filter adjusted: dropping %s", ", ".join(sorted(dropped)) or "nothing")
+
     logging.basicConfig(level=logging.INFO,
                         format="%(asctime)s %(levelname)-7s %(message)s",
                         datefmt="%H:%M:%S")
@@ -69,7 +82,9 @@ def main() -> None:
         # hidden trees like .broken/ must never reach the plan
         if not any(part.startswith(".") for part in p.relative_to(source).parts)
     )
-    catalog = load_catalog(args.catalog)
+    catalog = load_catalog(args.catalog, dropped=dropped)
+    if dropped:
+        log.info("Dropped systems: %s", ", ".join(sorted(dropped)))
     audit = args.audit or (args.library / "sorter_applied.jsonl")
 
     provenance = None