refactor: extract IPC channel names into a single source of truth

Duplicate raw string literals across handlers.ts, preload/index.ts made
typos undetectable at compile time and renames a multi-file grep problem.
A single channels.ts now owns all channel names; both files import from it.

Also fixes two bugs found during testing:
- LoginScreen and AccountScreen buttons were not triggerable via gamepad
  A-button: synthetic KeyboardEvents are untrusted and don't fire native
  button clicks. Added explicit keydown handlers that call the action directly.
- AppShell loading overlay could disappear while hlsPayload was still null
  if the playback:event 'started' IPC message arrived before playback:hls-url.
  Overlay now stays visible until hlsPayload is set, regardless of playState.

src/main/ipc/channels.ts

@@ -0,0 +1,36 @@
+export const IPC = {
+  appQuit: 'app:quit',
+  authStatus: 'auth:get-status',
+  authStart: 'auth:start-device-flow',
+  authCancel: 'auth:cancel',
+  authLogout: 'auth:logout',
+  authConfigured: 'auth:is-configured',
+  /** main → renderer */
+  authEvent: 'auth:event',
+
+  twitchGetFollowed: 'twitch:get-followed',
+  twitchGetOwnUser: 'twitch:get-own-user',
+  twitchGetVideos: 'twitch:get-videos',
+  twitchGetTopGames: 'twitch:get-top-games',
+  twitchGetTopStreams: 'twitch:get-top-streams',
+  twitchGetVodChapters: 'twitch:get-vod-chapters',
+  historyGetProgress: 'history:get-progress',
+
+  playbackStartLive: 'playback:start-live',
+  playbackStartVod: 'playback:start-vod',
+  playbackStop: 'playback:stop',
+  playbackPause: 'playback:pause',
+  playbackReportPosition: 'playback:report-position',
+  playbackGetQualities: 'playback:get-qualities',
+  /** main → renderer */
+  playbackEvent: 'playback:event',
+  /** main → renderer: HLS-URL + Metadaten für den Renderer-seitigen Video-Player */
+  playbackHlsUrl: 'playback:hls-url',
+
+  appGetCacheSize: 'app:get-cache-size',
+  appClearCache: 'app:clear-cache',
+  appSetHlsCacheEnabled: 'app:set-hls-cache-enabled',
+
+  /** main → renderer */
+  gamepadInput: 'gamepad-input'
+} as const

src/main/ipc/handlers.ts

@@ -8,40 +8,9 @@ import type { PlaybackService } from '../playback/playbackService'
 import type { HlsUrlPayload } from '../playback/playbackService'
 import type { PlaybackEvent } from '../playback/types'
 import { getProgressMap } from '../store/historyRepo'
+import { IPC } from './channels'
 
-export const IPC = {
-  appQuit: 'app:quit',
-  authStatus: 'auth:get-status',
-  authStart: 'auth:start-device-flow',
-  authCancel: 'auth:cancel',
-  authLogout: 'auth:logout',
-  authConfigured: 'auth:is-configured',
-  /** main → renderer */
-  authEvent: 'auth:event',
-
-  twitchGetFollowed: 'twitch:get-followed',
-  twitchGetOwnUser: 'twitch:get-own-user',
-  twitchGetVideos: 'twitch:get-videos',
-  twitchGetTopGames: 'twitch:get-top-games',
-  twitchGetTopStreams: 'twitch:get-top-streams',
-  twitchGetVodChapters: 'twitch:get-vod-chapters',
-  historyGetProgress: 'history:get-progress',
-
-  playbackStartLive: 'playback:start-live',
-  playbackStartVod: 'playback:start-vod',
-  playbackStop: 'playback:stop',
-  playbackPause: 'playback:pause',
-  playbackReportPosition: 'playback:report-position',
-  playbackGetQualities: 'playback:get-qualities',
-  /** main → renderer */
-  playbackEvent: 'playback:event',
-  /** main → renderer: HLS-URL + Metadaten für den Renderer-seitigen Video-Player */
-  playbackHlsUrl: 'playback:hls-url',
-
-  appGetCacheSize: 'app:get-cache-size',
-  appClearCache: 'app:clear-cache',
-  appSetHlsCacheEnabled: 'app:set-hls-cache-enabled'
-} as const
+export { IPC }
 
 export function registerIpcHandlers(
   auth: AuthService,