feat(wiki): add event item flag and decouple pokemon display ID

Add `is_event_item` to pokemon, items, and habitats.
Separate internal `id` and `display_id` for pokemon to allow event variants.
Update frontend forms and views to support the new fields.

frontend/src/views/PokemonList.vue

@@ -134,7 +134,7 @@ watch(query, loadPokemon);
       <EntityCard
         v-for="item in pokemon"
         :key="item.id"
-        :title="`#${item.id} ${item.name}`"
+        :title="`#${item.displayId} ${item.name}`"
         :to="`/pokemon/${item.id}`"
         :image="pokemonCardImage(item)"
       />