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/version_groups.json

@@ -391,5 +391,19 @@
         "color": "#A96EEC"
       }
     }
+  },
+  "legends-z-a": {
+    "versions": ["legends-z-a"],
+    "generation": 9,
+    "region": "lumiose",
+    "region_id": 0,
+    "games": {
+      "legends-z-a": {
+        "name": "Pokemon Legends: Z-A",
+        "slug": "legends-z-a",
+        "release_year": 2025,
+        "color": "#3A7BDB"
+      }
+    }
   }
 }