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/api/encounters.ts

@@ -24,6 +24,7 @@ export function deleteEncounter(id: number): Promise<void> {
   return api.del(`/encounters/${id}`)
 }
 
-export function fetchEvolutions(pokemonId: number): Promise<Evolution[]> {
-  return api.get(`/pokemon/${pokemonId}/evolutions`)
+export function fetchEvolutions(pokemonId: number, region?: string): Promise<Evolution[]> {
+  const params = region ? `?region=${encodeURIComponent(region)}` : ''
+  return api.get(`/pokemon/${pokemonId}/evolutions${params}`)
 }

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 = () => {

frontend/src/components/admin/EvolutionFormModal.tsx

@@ -29,6 +29,7 @@ export function EvolutionFormModal({
   const [item, setItem] = useState(evolution?.item ?? '')
   const [heldItem, setHeldItem] = useState(evolution?.heldItem ?? '')
   const [condition, setCondition] = useState(evolution?.condition ?? '')
+  const [region, setRegion] = useState(evolution?.region ?? '')
 
   const handleSubmit = (e: FormEvent) => {
     e.preventDefault()
@@ -41,6 +42,7 @@ export function EvolutionFormModal({
       item: item || null,
       heldItem: heldItem || null,
       condition: condition || null,
+      region: region || null,
     })
   }
 
@@ -119,6 +121,16 @@ export function EvolutionFormModal({
           className="w-full px-3 py-2 border rounded-md dark:bg-gray-700 dark:border-gray-600"
         />
       </div>
+      <div>
+        <label className="block text-sm font-medium mb-1">Region</label>
+        <input
+          type="text"
+          value={region}
+          onChange={(e) => setRegion(e.target.value)}
+          placeholder="e.g. alola (blank = all regions)"
+          className="w-full px-3 py-2 border rounded-md dark:bg-gray-700 dark:border-gray-600"
+        />
+      </div>
     </FormModal>
   )
 }

frontend/src/hooks/useEncounters.ts

@@ -43,10 +43,10 @@ export function useDeleteEncounter(runId: number) {
   })
 }
 
-export function useEvolutions(pokemonId: number | null) {
+export function useEvolutions(pokemonId: number | null, region?: string) {
   return useQuery({
-    queryKey: ['evolutions', pokemonId],
-    queryFn: () => fetchEvolutions(pokemonId!),
+    queryKey: ['evolutions', pokemonId, region],
+    queryFn: () => fetchEvolutions(pokemonId!, region),
     enabled: pokemonId !== null,
   })
 }

frontend/src/pages/RunDashboard.tsx

@@ -242,6 +242,7 @@ export function RunDashboard() {
           }}
           onClose={() => setSelectedEncounter(null)}
           isPending={updateEncounter.isPending}
+          region={run?.game.region}
         />
       )}
 

frontend/src/pages/RunEncounters.tsx

@@ -748,6 +748,7 @@ export function RunEncounters() {
           }}
           onClose={() => setSelectedTeamEncounter(null)}
           isPending={updateEncounter.isPending}
+          region={run?.game.region}
         />
       )}
 

frontend/src/types/admin.ts

@@ -86,6 +86,7 @@ export interface EvolutionAdmin {
   item: string | null
   heldItem: string | null
   condition: string | null
+  region: string | null
 }
 
 export interface PaginatedEvolutions {
@@ -103,6 +104,7 @@ export interface CreateEvolutionInput {
   item?: string | null
   heldItem?: string | null
   condition?: string | null
+  region?: string | null
 }
 
 export interface UpdateEvolutionInput {
@@ -113,4 +115,5 @@ export interface UpdateEvolutionInput {
   item?: string | null
   heldItem?: string | null
   condition?: string | null
+  region?: string | null
 }

frontend/src/types/game.ts

@@ -93,6 +93,7 @@ export interface Evolution {
   item: string | null
   heldItem: string | null
   condition: string | null
+  region: string | null
 }
 
 export interface CreateRunInput {