Implement comprehensive doodle canvas feature with premium gating and vector storage

[Copilot]

This PR rebuilds and enhances the full-featured drawing canvas functionality from PR #22 on top of the latest main branch, delivering a complete doodle system with vector-based storage, thumbnail generation, and seamless note integration.

🎨 Drawing Canvas Features

The enhanced drawing canvas provides a complete digital art experience:

• Full drawing toolkit: Pen and eraser tools with smooth stroke rendering using custom painter
• Color palette: 6 basic colors available to all users, plus 8 premium colors for upgraded accounts
• Brush sizing: 3 basic brush sizes (1px, 2px, 4px) free, with 3 additional premium sizes (6px, 8px, 12px)
• Premium tools: Highlighter with transparency effects and brush tool with rounded caps
• Undo/redo system: 50-level stroke-based history with visual feedback
• Auto-save functionality: Background saving with unsaved changes detection and user prompts

🔒 Premium Feature Gating

The implementation uses a non-disruptive premium model that enhances rather than blocks:

// Basic tools always available
final List<Color> _basicColors = [
  Colors.black, Colors.red, Colors.blue, 
  Colors.green, Colors.orange, Colors.purple,
];

// Premium tools shown with lock indicators
final List<String> _premiumTools = ['highlighter', 'brush'];

Premium users get access to advanced tools like highlighter and brush, while free users can create complete drawings with the core toolset.

💾 Vector-Based Storage System

Doodles are stored as vector data preserving complete editability:

class DoodleData {
  final List<DoodleLayer> layers;
  final Size canvasSize;
  final Color backgroundColor;
  final DateTime createdAt;
  final DateTime updatedAt;
}

class DoodleStroke {
  final List<Offset> points;
  final Color color;
  final double width;
  final String toolType; // pen, eraser, highlighter, brush
}

This approach maintains full drawing fidelity while enabling features like undo/redo and future layer support.

🖼️ Thumbnail Generation & Integration

The system automatically generates PNG thumbnails for doodle previews:

• Scalable rendering: Maintains aspect ratios while fitting target dimensions
• Tool-aware effects: Proper transparency for highlighter, stroke caps for brush tools
• Memory efficient: Widget-based caching with placeholder fallbacks
• Edit-in-place: Tap any thumbnail to reopen the full drawing canvas

🔗 Note Integration

Doodles integrate seamlessly with the existing note system:

• Attachment workflow: Doodles are treated as first-class attachments alongside images and files
• Reference insertion: Automatic doodle references inserted in note content: 🎨 [Doodle](path/to/doodle.json)
• Display widget: Grid and preview modes showing thumbnails with stroke counts and edit buttons
• Cleanup handling: Automatic removal of doodle files when notes are deleted

🏗️ Architecture & Compatibility

The implementation maintains full backward compatibility:

• Dual model support: Both legacy note_model.dart and new note.dart support doodle paths
• Extended attachment system: AttachmentType.doodle added with vector data and thumbnail fields
• Repository integration: CRUD operations for doodle persistence in organized app directory structure
• Service layer: Doodle operations integrated into existing NotesService with proper error handling

🧪 Testing Coverage

Comprehensive test suite ensures reliability:

• Model serialization: Complete JSON round-trip testing for all doodle data structures
• Integration workflows: Full create → save → load → edit → delete testing
• Service operations: CRUD operations, error handling, and edge cases
• Multiple doodle support: Independent management of multiple doodles per note

📱 User Experience

The implementation prioritizes smooth user interactions:

• Haptic feedback: Stroke completion and UI interactions provide tactile responses
• Visual feedback: Save status indicators, tool selection highlights, unsaved changes warnings
• Error handling: User-friendly error messages with recovery options
• Performance optimization: Efficient stroke rendering and memory management

This feature transforms QuickNote Pro into a comprehensive note-taking and digital art platform while maintaining the app's core simplicity and performance standards.

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[Copilot]

Pull Request Overview

This PR implements a comprehensive doodle canvas feature that enables users to create, edit, and manage digital drawings within notes. The feature includes premium gating for advanced tools, vector-based storage for full editability, automatic thumbnail generation, and seamless integration with the existing note system.

Key changes include:

• Complete drawing canvas with pen, eraser, and premium tools (highlighter, brush)
• Vector-based doodle storage system with JSON serialization
• Thumbnail generation service for doodle previews
• Premium feature gating with non-disruptive UI design

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/services/notes_service_doodle_integration_test.dart	Integration tests for complete doodle workflow including CRUD operations
test/models/note_model_doodle_test.dart	Unit tests for Note model with doodle path support
test/models/doodle_data_test.dart	Comprehensive tests for doodle data models and JSON serialization
lib/widgets/doodle_display_widget.dart	Display widget for doodle thumbnails with editing capability
lib/services/notes/notes_service.dart	Service layer extensions for doodle CRUD operations
lib/services/doodle_thumbnail_service.dart	Service for generating PNG thumbnails from vector doodle data
lib/repositories/notes_repository.dart	Repository layer for doodle file persistence
lib/presentation/note_creation_editor/widgets/drawing_canvas_widget.dart	Complete drawing canvas implementation with premium features
lib/presentation/note_creation_editor/note_creation_editor.dart	Integration of doodle references into note content
lib/models/note_model.dart	Extended Note model with doodle paths support
lib/models/note.dart	Enhanced attachment system with doodle support
lib/models/doodle_data.dart	Core vector data models for strokes, layers, and canvas
lib/models/attachment.dart	Extended attachment model with doodle-specific fields

[mikaelkraft]

Complete doodle implementation. Correct