fix: resolve Quick Prompt popup visibility and model picker issues

- Replace translucent glass background with solid surface-1 color;
  backdrop-filter does not work with transparent BrowserWindows on
  Windows, leaving the panel nearly invisible
- Add data-quickprompt body attribute to quickprompt.html and CSS
  overrides to ensure body/root are truly transparent, eliminating
  the visible rectangle behind the rounded panel
- Remove overflow-hidden from qp-panel so model selector dropdown
  is no longer clipped; the dropdown was positioned absolute and
  rendered entirely outside the panel bounds
- Change ModelSelector to open downward (top-full) instead of upward
  (bottom-full) for natural command-bar flow
- Update dropdown animation direction to match downward opening
- Increase blur handler delay to 200ms for safer dropdown interactions

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/windows/createQuickPromptWindow.ts

@@ -44,14 +44,14 @@ export function createQuickPromptWindow(): BrowserWindowType {
   // Hide on blur — but only if the window itself loses focus (not from
   // devtools or transient focus changes during show/hide).
   window.on('blur', () => {
-    // Small delay: avoid hiding during transient focus shifts (e.g. model
-    // selector dropdown causing a brief blur → refocus cycle).
+    // Longer delay: avoid hiding during transient focus shifts when
+    // interacting with model selector dropdown or other UI elements.
     setTimeout(() => {
       if (window.isVisible() && !window.isFocused()) {
         window.webContents.send('quick-prompt:hide');
         window.hide();
       }
-    }, 100);
+    }, 200);
   });
 
   return window;