feat(frontend): kontrakt danych i typowany klient API

- types/status.ts spisuje kształt odpowiedzi /api/status oraz pakietów
  rozgłaszanych po WebSockecie. Dotąd struktura tych danych istniała
  wyłącznie w głowie autora i w rozsianych po kodzie odwołaniach.
- api/client.ts zbiera wszystkie adresy endpointów w jednym miejscu i
  ujednolica obsługę błędów: pole "detail" z odpowiedzi FastAPI trafia do
  wyjątku ApiError, więc warstwa widoku dostaje gotowy komunikat.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/api/client.ts

@@ -0,0 +1,59 @@
+/** Cienka warstwa nad REST API bota - jedno miejsce, w którym znane są adresy. */
+
+import type { BotStatus, UploadedFile } from '@/types/status'
+
+export class ApiError extends Error {}
+
+async function request<T>(path: string, init?: RequestInit): Promise<T> {
+  const response = await fetch(path, init)
+  const payload = await response.json().catch(() => null)
+
+  if (!response.ok) {
+    const detail = payload && typeof payload.detail === 'string' ? payload.detail : response.statusText
+    throw new ApiError(detail || 'Żądanie nie powiodło się')
+  }
+  return payload as T
+}
+
+function post<T>(path: string, body?: unknown): Promise<T> {
+  return request<T>(path, {
+    method: 'POST',
+    headers: body === undefined ? undefined : { 'Content-Type': 'application/json' },
+    body: body === undefined ? undefined : JSON.stringify(body),
+  })
+}
+
+export const api = {
+  status: () => request<BotStatus>('/api/status'),
+
+  connect: (channelId: string) => post('/api/connect', { channel_id: channelId }),
+  disconnect: () => post('/api/disconnect'),
+
+  play: (query: string) => post('/api/play', { query }),
+  playFile: (filename: string) => post('/api/play_file', { filename }),
+  pause: () => post('/api/pause'),
+  resume: () => post('/api/resume'),
+  skip: () => post('/api/skip'),
+  stop: () => post('/api/stop'),
+  setVolume: (volume: number) => post('/api/volume', { volume }),
+  cycleLoop: () => post<{ mode: 'off' | 'playlist' | 'single' }>('/api/loop_cycle'),
+
+  jump: (index: number) => post('/api/jump', { index }),
+  remove: (id: string) => post('/api/remove', { id }),
+  reorder: (queueIds: string[]) => post('/api/reorder', { queue_ids: queueIds }),
+  setTrackPlays: (id: string, plays: number) => post('/api/queue/plays', { id, plays }),
+
+  uploads: () => request<{ files: UploadedFile[] }>('/api/uploads'),
+  deleteUpload: (filename: string) =>
+    request(`/api/uploads/${encodeURIComponent(filename)}`, { method: 'DELETE' }),
+  upload: (file: File) => {
+    const form = new FormData()
+    form.append('file', file)
+    return request<{ filename: string }>('/api/upload', { method: 'POST', body: form })
+  },
+
+  setDefaultPlays: (defaultPlays: number) =>
+    post('/api/settings/default_plays', { default_plays: defaultPlays }),
+  setLogChannel: (guildId: string, channelId: string) =>
+    post('/api/settings/text_channel', { guild_id: guildId, channel_id: channelId }),
+}

frontend/src/types/status.ts

@@ -0,0 +1,78 @@
+/** Kształt danych zwracanych przez /api/status oraz rozgłaszanych po WebSockecie. */
+
+export interface VoiceChannel {
+  guild_id: string
+  guild_name: string
+  channel_id: string
+  channel_name: string
+}
+
+export interface TextChannel {
+  channel_id: string
+  channel_name: string
+}
+
+export interface GuildSettings {
+  guild_id: string
+  guild_name: string
+  text_channels: TextChannel[]
+  active_notification_channel_id: string | null
+}
+
+export interface CurrentTrack {
+  id: string
+  title: string
+  url: string | null
+  duration: number | null
+  elapsed: number
+  plays_left: number
+}
+
+export interface QueueTrack {
+  id: string
+  title: string
+  url: string | null
+  plays_left: number
+}
+
+export interface HistoryTrack {
+  id: string
+  title: string
+  url: string | null
+  duration: number | null
+  is_local: boolean
+  filepath: string | null
+}
+
+export interface UploadedFile {
+  filename: string
+  size_mb: number
+  mtime: number
+}
+
+export interface BotStatus {
+  playing: boolean
+  paused: boolean
+  loop_single: boolean
+  loop_playlist: boolean
+  volume: number
+  current: CurrentTrack | null
+  queue: QueueTrack[]
+  queue_index: number
+  history: HistoryTrack[]
+  voice_channels: VoiceChannel[]
+  active_voice_channel: VoiceChannel | null
+  text_channels: VoiceChannel[]
+  active_text_channel_id: string | null
+  guilds: GuildSettings[]
+  default_plays: number
+}
+
+export type LoopMode = 'off' | 'playlist' | 'single'
+
+export function loopModeOf(status: BotStatus | null): LoopMode {
+  if (!status) return 'off'
+  if (status.loop_single) return 'single'
+  if (status.loop_playlist) return 'playlist'
+  return 'off'
+}