feat(ui): transparent window and rounded corners for Tauri

- Add drag-region helpers (.tauri-drag/.tauri-no-drag)\n- Apply transparent background and clip-path rounding\n- Define theme tokens and typography utilities\n- Refine scrollbars and markdown editor/prose styles

Author: 123vivekr

src/styles.css

@@ -10,6 +10,15 @@ html, body {
   background-color: rgba(0, 0, 0, 0);
 }
 
+/* Tauri drag region helpers */
+.tauri-drag {
+  -webkit-app-region: drag;
+}
+
+.tauri-no-drag {
+  -webkit-app-region: no-drag;
+}
+
 /* Apply rounded corners and background to body */
 body {
   border-radius: var(--radius-lg);
@@ -966,4 +975,4 @@ code::-webkit-scrollbar-thumb:hover {
 
 .image-move-to-input {
   animation: moveToInput 0.8s ease-in-out forwards;
-} 
+}