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/widgets/bottom_nav.dart

@@ -0,0 +1,71 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
+import '../bloc/app_bloc.dart';
+import '../bloc/app_event.dart';
+import '../models/models.dart';
+
+class BottomNav extends StatelessWidget {
+  final AppScreen currentScreen;
+
+  const BottomNav({super.key, required this.currentScreen});
+
+  @override
+  Widget build(BuildContext context) {
+    final navItems = [
+      (id: AppScreen.library, label: 'Полка', icon: Icons.menu_book),
+      (id: AppScreen.categories, label: 'Категории', icon: Icons.category),
+      (id: AppScreen.wishlist, label: 'Вишлист', icon: Icons.bookmark),
+      (id: AppScreen.settings, label: 'Настройки', icon: Icons.settings),
+    ];
+
+    return Container(
+      decoration: BoxDecoration(
+        color: Colors.black.withValues(alpha: 0.85),
+        border: Border(
+          top: BorderSide(color: Colors.white.withValues(alpha: 0.05), width: 1),
+        ),
+      ),
+      child: SafeArea(
+        child: SizedBox(
+          height: 64,
+          child: Row(
+            mainAxisAlignment: MainAxisAlignment.spaceAround,
+            children: navItems.map((item) {
+              final isSelected = currentScreen == item.id;
+              return Expanded(
+                child: GestureDetector(
+                  onTap: () {
+                    context.read<AppBloc>().add(ScreenChanged(item.id));
+                  },
+                  child: Column(
+                    mainAxisAlignment: MainAxisAlignment.center,
+                    children: [
+                      Icon(
+                        item.icon,
+                        color: isSelected
+                            ? const Color(0xFF17CF54)
+                            : Colors.grey.withValues(alpha: 0.6),
+                        size: 24,
+                      ),
+                      const SizedBox(height: 2),
+                      Text(
+                        item.label,
+                        style: TextStyle(
+                          fontSize: 10,
+                          fontWeight: FontWeight.w500,
+                          color: isSelected
+                              ? const Color(0xFF17CF54)
+                              : Colors.grey.withValues(alpha: 0.6),
+                        ),
+                      ),
+                    ],
+                  ),
+                ),
+              );
+            }).toList(),
+          ),
+        ),
+      ),
+    );
+  }
+}