Add Pokemon Legends: Z-A to the game list

Add version group entry with region_id 0 (no PokeAPI region) and region
"lumiose". The Go fetch tool now skips route fetching for region_id 0 so
manually provided data won't be overwritten by re-runs. Includes
placeholder data file and box art.

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

backend/src/app/seeds/run.py

@@ -40,7 +40,7 @@ GAME_FILES = [
     # Gen 8
     "sword", "shield", "brilliant-diamond", "shining-pearl", "legends-arceus",
     # Gen 9
-    "scarlet", "violet",
+    "scarlet", "violet", "legends-z-a",
 ]