[EPIC] Implement Preset Save Functionality

[SeamusMullan]

Add ability to save current configuration as a preset.

Objectives

• Add "Save as Preset" button
• Implement preset name dialog
• Save configuration to XML
• Store in user预设 directory

Linked Tasks

• Add "Save as Preset" to File menu
• Create preset name input dialog
• Implement XML serialization
• Create ~/.plugin_configurator/presets/ directory
• Add error handling

Success Criteria

• Presets save correctly to XML
• All settings included in saved file
• Directory created if doesn't exist
• Error handling works

Timeline

• Start: 2026-04-27
• End: 2026-04-30
• Duration: 4 days