refactor: remove legacy volume_boost references in favor of generalized player effects API

frontend/src/api/client.ts

@@ -55,8 +55,6 @@ export const api = {
   skip: () => post('/api/skip'),
   stop: () => post('/api/stop'),
   setVolume: (volume: number) => post('/api/volume', { volume }),
-  setVolumeBoost: (enabled?: boolean) =>
-    post<{ status: string; volume_boost: boolean }>('/api/volume_boost', { enabled }),
   toggleEffect: (effectId: string, enabled?: boolean) =>
     post<{ status: string; effect_id: string; active: boolean; active_effects: string[] }>(
       '/api/effects/toggle',

frontend/src/types/status.ts

@@ -65,8 +65,6 @@ export interface BotStatus {
   loop_single: boolean
   loop_playlist: boolean
   volume: number
-  volume_boost?: boolean
-  volume_boost_multiplier?: number
   effects?: PlayerEffect[]
   active_effects?: string[]
   current: CurrentTrack | null