feat: add Tauri state persistence and BvCli trait

- Add Tauri storage adapter for Zustand (tauri-storage.ts)
- Add read_state, write_state, clear_state Tauri commands
- Wire focus-store and nav-store to use Tauri persistence
- Add BvCli trait for bv CLI mocking with response types
- Add BvError and McError conversion for bv errors
- Add cleanup_tmp_files tests for bridge
- Fix linter-introduced tauri_specta::command issues

Closes bd-2x6, bd-gil, bd-3px

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src-tauri/Cargo.toml

@@ -30,6 +30,9 @@ dirs = "5"
 notify = "7"
 tauri-plugin-global-shortcut = "2"
 libc = "0.2"
+specta = { version = "=2.0.0-rc.22", features = ["derive"] }
+tauri-specta = { version = "=2.0.0-rc.21", features = ["derive", "typescript"] }
+specta-typescript = "0.0.9"
 
 [dev-dependencies]
 tempfile = "3"