style: apply rustfmt, fix clippy warnings, and minor code cleanup

Reformat Rust code with rustfmt, suppress clippy::too_many_arguments
for Tauri IPC commands, derive Default for AppSettings, fix unused
variable pattern in TableDataView, and add unit tests for utils.

src-tauri/src/lib.rs

@@ -57,9 +57,13 @@ pub fn run() {
                 let mcp_state = state.clone();
                 tauri::async_runtime::spawn(async move {
                     *mcp_state.mcp_running.write().await = true;
-                    if let Err(e) =
-                        mcp::start_mcp_server(mcp_state.clone(), connections_path, mcp_port, shutdown_rx)
-                            .await
+                    if let Err(e) = mcp::start_mcp_server(
+                        mcp_state.clone(),
+                        connections_path,
+                        mcp_port,
+                        shutdown_rx,
+                    )
+                    .await
                     {
                         log::error!("MCP server error: {}", e);
                     }