feat(shell): add Dashboard nav entry; swap fake "D" mark for real logo

The sidebar header used a gradient "D" tile as a placeholder. Now it
uses the actual dragon-coiled-D logo so the brand reads consistently
between the launcher hero and the chrome.

Also adds a 'Dashboard' nav item directly under 'Home' so the
operations view is one click away.

services/web-ui/public/shell.jsx

@@ -2,6 +2,7 @@
 
 const NAV_TREE = [
   { id: "home", label: "Home", icon: "home" },
+  { id: "dashboard", label: "Dashboard", icon: "library" },
   { id: "library", label: "Library", icon: "library" },
   { id: "projects", label: "Projects", icon: "folder" },
   {
@@ -96,8 +97,8 @@ function Sidebar({ active, onNavigate }) {
 
   return (
     <aside className="sidebar">
-      <div className="sidebar-header">
-        <div className="brand-mark">D</div>
+      <div className="sidebar-header" onClick={() => onNavigate('home')} style={{ cursor: 'pointer' }} title="Home">
+        <img className="brand-logo" src="img/dragon-logo.png" alt="Dragonflight" draggable="false" />
         <div>
           <div className="brand-name">Dragonflight</div>
         </div>