Vault list was stored only in React useState, lost on every app restart
or update. Now persisted to ~/.config/com.laputa.app/vaults.json via
Rust backend commands (load_vault_list, save_vault_list).
- Add vault_list.rs module with VaultEntry/VaultList types and JSON I/O
- Register load_vault_list/save_vault_list Tauri commands
- Extract vaultListStore.ts utility for frontend persistence calls
- Rewrite useVaultSwitcher to load on mount and persist on change
- Show unavailable vaults greyed out with warning icon instead of
silently removing them
- Add mock handlers for browser/test environments
- Add useVaultSwitcher tests covering persistence, availability, dedup
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>