Fix book duration to exclude disabled audio tracks

Add Book.updateDuration() which sums the included (non-excluded) audio
files, and call it from updateTracks before saving so disabling a track
updates the stored duration.

Fixes #5311

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/controllers/LibraryItemController.js

@@ -507,6 +507,8 @@ class LibraryItemController {
 
     req.libraryItem.media.audioFiles = updatedAudioFiles
     req.libraryItem.media.changed('audioFiles', true)
+    // Recompute duration so disabled (excluded) tracks no longer count toward the total
+    req.libraryItem.media.updateDuration()
     await req.libraryItem.media.save()
 
     SocketAuthority.libraryItemEmitter('item_updated', req.libraryItem)

server/models/Book.js

@@ -261,6 +261,19 @@ class Book extends Model {
     return this.audioFiles.filter((af) => !af.exclude)
   }
 
+  /**
+   * Recalculate the book duration from the included (non-excluded) audio files.
+   * Sets `this.duration` and returns whether it changed.
+   *
+   * @returns {boolean}
+   */
+  updateDuration() {
+    const newDuration = this.includedAudioFiles.reduce((total, af) => total + (isNaN(af.duration) ? 0 : Number(af.duration)), 0)
+    if (this.duration === newDuration) return false
+    this.duration = newDuration
+    return true
+  }
+
   get hasMediaFiles() {
     return !!this.hasAudioTracks || !!this.ebookFile
   }