style: translate all remaining German code comments to English

German comments had survived the earlier translation pass. Mixing
languages in comments creates inconsistency and makes the codebase
harder to read for non-German contributors.

src/main/auth/authService.ts

@@ -49,8 +49,8 @@ export class AuthService extends EventEmitter {
   }
 
   /**
-   * Startet den Device Code Flow. Liefert die Anzeigedaten sofort zurück
-   * und pollt im Hintergrund. Statuswechsel werden als 'auth-event' emittiert.
+   * Starts the Device Code Flow. Returns display data immediately
+   * and polls in the background. Status changes are emitted as 'auth-event'.
    */
   async startDeviceFlow(): Promise<DeviceFlowStartInfo> {
     if (!this.isConfigured()) {
@@ -86,8 +86,8 @@ export class AuthService extends EventEmitter {
   }
 
   /**
-   * Liefert ein gültiges Access-Token, refresht falls nötig.
-   * Wird vom Helix-Client benutzt.
+   * Returns a valid access token, refreshing it if necessary.
+   * Used by the Helix client.
    */
   async getValidAccessToken(): Promise<string | null> {
     if (!this.tokens) return null
@@ -100,7 +100,7 @@ export class AuthService extends EventEmitter {
       await saveTokens(this.tokens)
       return this.tokens.accessToken
     } catch {
-      // Refresh fehlgeschlagen → User muss sich neu einloggen.
+      // Refresh failed — user must log in again.
       this.tokens = null
       await clearTokens()
       return null