Introduce SerenaDashboardViewer based on pywebview

Shows the dashboard in a separate application window we can control,
replacing the use of the webbrowser module to open the dashboard in
a browser tab

pyproject.toml

@@ -36,6 +36,8 @@ dependencies = [
   "tiktoken>=0.9.0",
   "anthropic>=0.54.0",
   "beautifulsoup4>=4.14.2",
+  "pywebview>=6.1",
+  "pystray>=0.19.5",
 ]
 
 [[tool.uv.index]]