Rename app to Nook (display name only)

Changes the user-visible name from "ABS Client" to "Nook" across the
iOS home screen, macOS Dock/menu bar, login header, sidebar header, and
README. Bundle ID (com.local.ABS-Client), keychain key, and background
download session ID are intentionally left unchanged so the existing
App Store listing (ID 6770326901) updates in place — installed users
keep the app, stored credentials, and downloads.

- Build settings: INFOPLIST_KEY_CFBundleDisplayName, CFBundleName,
  PRODUCT_NAME → "Nook" (Debug + Release); built app is now Nook.app
- Info-iOS.plist: CFBundleDisplayName + CFBundleName → "Nook"
- Localizable.strings (de + en): login.title + sidebar.app_title → "Nook"
- LoginView: hardcoded headers → "Nook"
- README: branding text → "Nook" (git repo URLs and App Store URL
  unchanged — repo and listing rename happen separately)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ABS Client/Audiobookshelf swift.xcodeproj/xcshareddata/xcschemes/DownloadWidgetExtensionExtension.xcscheme

@@ -31,7 +31,7 @@
             <BuildableReference
                BuildableIdentifier = "primary"
                BlueprintIdentifier = "39614D0A2FB4D44400DBEF5E"
-               BuildableName = "ABS Client.app"
+               BuildableName = "Nook.app"
                BlueprintName = "Audiobookshelf swift"
                ReferencedContainer = "container:Audiobookshelf swift.xcodeproj">
             </BuildableReference>
@@ -62,7 +62,7 @@
          <BuildableReference
             BuildableIdentifier = "primary"
             BlueprintIdentifier = "39614D0A2FB4D44400DBEF5E"
-            BuildableName = "ABS Client.app"
+            BuildableName = "Nook.app"
             BlueprintName = "Audiobookshelf swift"
             ReferencedContainer = "container:Audiobookshelf swift.xcodeproj">
          </BuildableReference>
@@ -98,7 +98,7 @@
          <BuildableReference
             BuildableIdentifier = "primary"
             BlueprintIdentifier = "39614D0A2FB4D44400DBEF5E"
-            BuildableName = "ABS Client.app"
+            BuildableName = "Nook.app"
             BlueprintName = "Audiobookshelf swift"
             ReferencedContainer = "container:Audiobookshelf swift.xcodeproj">
          </BuildableReference>