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/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 {