* feat: improve save/load interface with custom names and metadata
- Add custom save name support with input validation
- Extend save metadata with avatar counts, protagonist info, and event count
- Add quick save button alongside named save option
- Enhance save list display with richer information
- Add sanitize_save_name and find_protagonist_name helpers
- Update API endpoints to support new features
- Add i18n translations for new UI elements
Closes#95
* test: add comprehensive tests for save custom name feature
- Add 37 tests for sanitize_save_name, find_protagonist_name
- Add tests for custom name API endpoints
- Add tests for enhanced metadata
- Fix unused NIcon import in SaveLoadPanel
- Add zh-TW translations for new save_load keys
* test(frontend): add SaveLoadPanel component tests
- Add 21 tests for SaveLoadPanel component
- Cover save mode, load mode, display, validation
- Mock naive-ui components, stores, and API
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