Add region picker for OpenSky default bounding box

Replace the free-text bounding-box field in the Web App OpenSky
settings with a grouped preset picker (World / Continents / Countries)
plus a Custom option that keeps the manual lamin,lomin,lamax,lomax
entry. Saved values that match a preset render as the friendly region
name, including in the locked/inherited display.

Change the API Server default bounding box to Europe to match the new
"Europe" preset.

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-BdIdzNiz.js"></script>
-    <link rel="stylesheet" crossorigin href="./assets/index-CYeDXsw9.css">
+    <script type="module" crossorigin src="./assets/index-CznFJTz4.js"></script>
+    <link rel="stylesheet" crossorigin href="./assets/index-D0ghlckk.css">
   </head>
   <body>
     <div id="app"></div>