Implement Save and Load Graph Functionality

# Implement Save and Load Graph Functionality

**Priority:** High

## Description
Users need the ability to save their graph configurations and load them later. This feature will improve user experience and enable sharing of graph configurations.

## Required Features
1. Save Functionality:
- [ ] Save current graph state
- [ ] Export to JSON format
- [ ] Local storage integration
- [ ] Optional graph naming

2. Load Functionality:
- [ ] Import from JSON file
- [ ] Load from local storage
- [ ] Validate imported data
- [ ] Handle loading errors

3. Sharing Features:
- [ ] Generate shareable URLs
- [ ] Graph state serialization
- [ ] Sample graph templates
- [ ] Import history

## Technical Specifications
- Use JSON for data format
- Implement data validation
- Add compression for large graphs
- Include version control for saved formats

## Security Considerations
- Validate imported data
- Sanitize graph names
- Set reasonable size limits
- Implement safe parsing

## Acceptance Criteria
- Graphs should save and load without data loss
- Error handling for invalid imports
- Intuitive UI for save/load operations
- Working share functionality

issue 中没有确定任何文件、测试或入口点。首先梳理图状态和保存/加载 UI 的处理位置，然后定义 JSON 格式、验证、存储、共享和错误处理的边界；完成的标准是所有列出的验收标准都能在不丢失数据的情况下运行。

由索引模型根据 Issue 内容生成。