Add Map settings toggle to show/hide live air traffic

Add a "Map settings" popover (gear button) on the Overview Live map with a
"Show live air traffic" switch, backed by a new client-side showAirTraffic
preference (default on, persisted in localStorage and synced like other
prefs). When off, the aircraft overlay clears and polling pauses to save
OpenSky credits; the count badge and caption reflect the hidden state.
Toggling on re-fetches immediately.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Web App/server/dist/index.html

@@ -35,8 +35,8 @@
       })()
     </script>
     <title>PilotVault — Control Panel</title>
-    <script type="module" crossorigin src="./assets/index-uk1cBykG.js"></script>
-    <link rel="stylesheet" crossorigin href="./assets/index-CoIRbg0g.css">
+    <script type="module" crossorigin src="./assets/index-Dk_VY0uv.js"></script>
+    <link rel="stylesheet" crossorigin href="./assets/index-Bvd5MzZB.css">
   </head>
   <body>
     <div id="app"></div>