Add "Open local folder" and "Create new vault" options to the vault picker dropdown. Uses tauri-plugin-dialog for native folder picker in Tauri mode, falls back to prompt() in browser mode. - Rust: add tauri-plugin-dialog, create_vault_dir command - Frontend: pickFolder utility, StatusBar UI, App.tsx handlers - Mock: create_vault_dir mock handler for browser testing Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>