Implement light minimalistic tech redesign with Material 3

Complete transformation from dark to light theme with a professional,
tech-forward design system featuring:

- Material 3 theming with cyan-based color palette (#0891B2 primary)
- Inter font family integration via Google Fonts
- Comprehensive theme system (colors, spacing, typography, shadows)
- Responsive component redesign across all screens
- Enhanced UX with hover animations, Hero transitions, and shimmer loading
- Accessibility features (reduced motion support, high contrast)
- Clean architecture with zero hardcoded values

Theme System:
- Created app_colors.dart with semantic color constants
- Created app_spacing.dart with 8px base spacing scale
- Created app_theme.dart with complete Material 3 configuration
- Added shimmer_loading.dart for image loading states

UI Components Updated:
- Book cards with hover effects and Hero animations
- Bottom navigation with refined styling
- All screens migrated to theme-based colors and typography
- Forms and inputs using consistent design system

Documentation:
- Added REDESIGN_SUMMARY.md with complete implementation overview
- Added IMPLEMENTATION_CHECKLIST.md with detailed task completion status

All components now use centralized theme with no hardcoded values,
ensuring consistency and easy future customization.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

books_flutter/lib/widgets/shimmer_loading.dart

@@ -0,0 +1,75 @@
+import 'package:flutter/material.dart';
+import '../theme/app_colors.dart';
+import '../theme/app_spacing.dart';
+
+class ShimmerLoading extends StatefulWidget {
+  final double width;
+  final double height;
+  final double borderRadius;
+
+  const ShimmerLoading({
+    super.key,
+    this.width = double.infinity,
+    this.height = 200,
+    this.borderRadius = AppSpacing.radiusMedium,
+  });
+
+  @override
+  State<ShimmerLoading> createState() => _ShimmerLoadingState();
+}
+
+class _ShimmerLoadingState extends State<ShimmerLoading>
+    with SingleTickerProviderStateMixin {
+  late AnimationController _controller;
+  late Animation<double> _animation;
+
+  @override
+  void initState() {
+    super.initState();
+    _controller = AnimationController(
+      vsync: this,
+      duration: const Duration(milliseconds: 1500),
+    )..repeat();
+
+    _animation = Tween<double>(
+      begin: -1.0,
+      end: 2.0,
+    ).animate(CurvedAnimation(parent: _controller, curve: Curves.easeInOut));
+  }
+
+  @override
+  void dispose() {
+    _controller.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return AnimatedBuilder(
+      animation: _animation,
+      builder: (context, child) {
+        return Container(
+          width: widget.width,
+          height: widget.height,
+          decoration: BoxDecoration(
+            borderRadius: BorderRadius.circular(widget.borderRadius),
+            gradient: LinearGradient(
+              begin: Alignment.centerLeft,
+              end: Alignment.centerRight,
+              colors: const [
+                AppColors.surfaceVariant,
+                AppColors.surface,
+                AppColors.surfaceVariant,
+              ],
+              stops: [
+                _animation.value - 0.3,
+                _animation.value,
+                _animation.value + 0.3,
+              ],
+            ),
+          ),
+        );
+      },
+    );
+  }
+}