refactor: restructure to core/ + ui/ with multi-threaded backend

ui/styles/app.css

@@ -0,0 +1,41 @@
+/* Global Styles for Graph Memory TUI */
+
+GraphMemoryApp {
+    background: $surface;
+    color: $text;
+}
+
+/* 全局Input样式 - 确保可见 */
+Input {
+    background: $surface-lighten-1;
+    color: $text;
+    border: solid $primary;
+}
+
+Input:focus {
+    border: double $accent;
+}
+
+LeftPanel {
+    width: 1fr;
+    dock: left;
+}
+
+RightPanel {
+    width: 70;
+    dock: right;
+    background: $panel;
+    overflow-y: auto;
+}
+
+RightPanel ScrollableContainer {
+    height: 1fr;
+    overflow-y: auto;
+}
+
+StatusBar {
+    dock: bottom;
+    height: 1;
+    background: $primary;
+    color: $text-primary;
+}