refactor: create separate BLoCs for each screen with comprehensive tests

- Created 8 separate BLoCs (Home, Library, BookDetails, AddBook, Scanner, Categories, Wishlist, Settings)
- Each BLoC has its own event, state, and bloc files
- Added 70 comprehensive tests covering all BLoC functionality
- All tests passing (70/70)
- Fixed linting issues and updated deprecated APIs
- Improved code organization and maintainability

bookshelf_flutter/lib/bloc/app_event.dart

@@ -0,0 +1,39 @@
+import '../models/models.dart';
+
+abstract class AppEvent {
+  const AppEvent();
+}
+
+class ScreenChanged extends AppEvent {
+  final AppScreen screen;
+  const ScreenChanged(this.screen);
+}
+
+class BookClicked extends AppEvent {
+  final Book book;
+  const BookClicked(this.book);
+}
+
+class AddBookClicked extends AppEvent {
+  const AddBookClicked();
+}
+
+class BookSaved extends AppEvent {
+  final Map<String, dynamic> bookData;
+  const BookSaved(this.bookData);
+}
+
+class BookDeleted extends AppEvent {
+  final String id;
+  const BookDeleted(this.id);
+}
+
+class BookDetected extends AppEvent {
+  final Map<String, dynamic> bookData;
+  const BookDetected(this.bookData);
+}
+
+class SearchChanged extends AppEvent {
+  final String query;
+  const SearchChanged(this.query);
+}