Add nullable region field to evolutions for regional form filtering

Regional evolutions (e.g., Pikachu → Alolan Raichu) only occur in specific
regions. This adds a nullable region column so the app can filter evolutions
by the game's region. When a regional evolution exists for a given trigger/item,
the non-regional counterpart is automatically hidden.

Full-stack: migration, model, schemas, API with region query param, seeder,
Go fetch tool, frontend types/API/hook/components, and admin form.

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

frontend/src/components/StatusChangeModal.tsx

@@ -10,6 +10,7 @@ interface StatusChangeModalProps {
   }) => void
   onClose: () => void
   isPending: boolean
+  region?: string
 }
 
 const typeColors: Record<string, string> = {
@@ -60,6 +61,7 @@ export function StatusChangeModal({
   onUpdate,
   onClose,
   isPending,
+  region,
 }: StatusChangeModalProps) {
   const { pokemon, currentPokemon, route, nickname, catchLevel, faintLevel, deathCause } =
     encounter
@@ -72,7 +74,8 @@ export function StatusChangeModal({
 
   const activePokemonId = currentPokemon?.id ?? pokemon.id
   const { data: evolutions, isLoading: evolutionsLoading } = useEvolutions(
-    showEvolve ? activePokemonId : null
+    showEvolve ? activePokemonId : null,
+    region,
   )
 
   const handleConfirmDeath = () => {