refactor(tauri): decompose lib command surface into domain modules

Split the large lib command module into nested app_api, cache, sync, and ui submodules while preserving command signatures and behavior. This keeps command responsibilities isolated and makes further extraction safer.

src-tauri/src/lib_commands/mod.rs

@@ -0,0 +1,11 @@
+use super::*;
+
+mod app_api;
+mod cache;
+mod sync;
+mod ui;
+
+pub(crate) use app_api::*;
+pub(crate) use cache::*;
+pub(crate) use sync::*;
+pub(crate) use ui::*;