Add section field to boss battles for run progression dividers

Adds a nullable `section` column to boss battles (e.g. "Main Story",
"Endgame") with dividers rendered in the run view between sections.
Admin UI gets a Section column in the table and a text input in the form.

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

frontend/src/types/admin.ts

@@ -147,6 +147,7 @@ export interface CreateBossBattleInput {
   order: number
   afterRouteId?: number | null
   location: string
+  section?: string | null
   spriteUrl?: string | null
 }
 
@@ -159,9 +160,15 @@ export interface UpdateBossBattleInput {
   order?: number
   afterRouteId?: number | null
   location?: string
+  section?: string | null
   spriteUrl?: string | null
 }
 
+export interface BossReorderItem {
+  id: number
+  order: number
+}
+
 export interface BossPokemonInput {
   pokemonId: number
   level: number

frontend/src/types/game.ts

@@ -151,6 +151,7 @@ export interface BossBattle {
   order: number
   afterRouteId: number | null
   location: string
+  section: string | null
   spriteUrl: string | null
   pokemon: BossPokemon[]
 }