Add keyboard shortcut system to xserial-gui

Introduce a centralized shortcut system with ShortcutAction enum and bindings table in shortcuts.rs. Global shortcuts are processed at the top of XserialApp::ui() before any widget rendering. Text input focus is detected via wants_keyboard_input() to suppress shortcuts when typing. Also fix pre-existing import ordering in panels/config.rs from cargo fmt.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

crates/xserial-gui/src/panels/config.rs

@@ -1,12 +1,12 @@
 use egui::{ComboBox, DragValue, ScrollArea, TextEdit, Ui};
 use xserial_client::config::{DecoderConfig, FramerConfig, PipelineConfig, SessionConfig};
+use xserial_core::protocol::Endian;
 use xserial_core::protocol::plot::{PlotFormat, SampleType};
 use xserial_core::protocol::text::TextEncoding;
-use xserial_core::protocol::Endian;
+use xserial_core::transport::TransportConfig;
 use xserial_core::transport::serial::{
     SerialDataBits, SerialFlowControl, SerialParity, SerialStopBits, SerialTransport,
 };
-use xserial_core::transport::TransportConfig;
 
 #[derive(Clone)]
 pub struct ConfigForm {