🔄 Implement JSONL Data Export/Import System for Pet Data Backup

[Copilot]

This PR implements a comprehensive JSONL Data Export/Import System for Petalytics, enabling users to backup and restore their pet data locally. This supports the "shell app" model where users maintain full ownership of their data and can migrate between sessions.

Key Features

DataExporter Class (src/lib/utils/data-export.ts)

• Export functionality: Individual pets or complete backup to JSONL format
• Import functionality: JSONL file parsing with comprehensive data validation
• Version compatibility: Built-in checking for future data migrations
• Privacy-first: All operations performed client-side with no cloud dependencies

DataManager UI Component (src/lib/components/ui/DataManager.svelte)

• Intuitive export/import interface integrated into Guardian Panel
• File upload with validation and user feedback
• Export options for individual pets or complete system backup
• Data format information and usage instructions

Enhanced Store Integration

• Extended pet helpers with getAllPets() and importPet() methods
• Added importGuardian() method to guardian helpers
• Seamless data merging during import operations

Data Format

The system uses JSONL (JSON Lines) format for structured data export:

{"version":"1.0.0"}
{"exportDate":"2024-01-01T12:00:00.000Z"}
{"pet":{"id":"buddy-123","name":"Buddy","breed":"Golden Retriever",...}}
{"aiAnalyses":{}}

This format ensures:

• Efficient processing of large datasets
• Human-readable structure for debugging
• Version compatibility for future migrations
• Preservation of all pet data including journal entries and AI analyses

User Interface

The Data Management section is seamlessly integrated into the Guardian Panel settings:

Users can:

• Export all data as a complete backup
• Export individual pets separately
• Import previously exported data files
• View data format specifications

Privacy & Security

• Local-only operations: All export/import happens client-side
• No cloud storage: Data never leaves the user's device
• User data ownership: Complete control over pet information
• Portable format: JSONL ensures data can be used across platforms

Technical Implementation

• TypeScript-based with full type safety
• Comprehensive error handling and validation
• Integration with existing Svelte stores
• Responsive UI design matching app aesthetic
• Build process verified with no compilation errors

This implementation fully addresses the requirements for local data backup/restore functionality while maintaining the privacy-first approach of the Petalytics application.

Fixes #13.

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