feat: refine management UI, connection diagnostics and local startup

Migrate the workspace to React and Ant Design, improve account forms and responsive layouts, support outbound diagnostics and SSH fingerprint confirmation, and persist the management startup port. Preserve database migrations, remove S3 settings storage, and improve gateway audit handling.

web/public/linkport.svg

@@ -1,8 +1,21 @@
 <svg xmlns="http://www.w3.org/2000/svg" width="64" height="64" viewBox="0 0 64 64" role="img" aria-labelledby="linkport-title">
   <title id="linkport-title">LinkPort</title>
-  <rect width="64" height="64" rx="15" fill="#1d4ed8" />
-  <path d="M25 49V16h13c8 0 13 5 13 12s-5 12-13 12H25" fill="none" stroke="#ffffff" stroke-width="5.5" stroke-linecap="round" stroke-linejoin="round" />
-  <path d="M11 28h14M25 49h22" fill="none" stroke="#67e8f9" stroke-width="4.5" stroke-linecap="round" />
-  <circle cx="11" cy="28" r="4" fill="#67e8f9" />
-  <circle cx="47" cy="49" r="4" fill="#67e8f9" />
+  <defs>
+    <linearGradient id="background" x1="8" y1="2" x2="56" y2="64" gradientUnits="userSpaceOnUse">
+      <stop stop-color="#398bff" />
+      <stop offset="0.52" stop-color="#1677ff" />
+      <stop offset="1" stop-color="#2445bd" />
+    </linearGradient>
+    <linearGradient id="connection" x1="13" y1="24" x2="34" y2="40" gradientUnits="userSpaceOnUse">
+      <stop stop-color="#baf8ff" />
+      <stop offset="1" stop-color="#6de5ee" />
+    </linearGradient>
+  </defs>
+  <rect width="64" height="64" rx="17" fill="url(#background)" />
+  <rect x="0.75" y="0.75" width="62.5" height="62.5" rx="16.25" fill="none" stroke="#fff" stroke-opacity="0.18" stroke-width="1.5" />
+  <g transform="rotate(-38 32 32)" fill="none" stroke-width="6" stroke-linecap="round" stroke-linejoin="round">
+    <path d="M29 24h-7a8 8 0 0 0 0 16h7" stroke="url(#connection)" />
+    <path d="M35 24h7a8 8 0 0 1 0 16h-7" stroke="#fff" />
+    <path d="M25 32h14" stroke="#fff" />
+  </g>
 </svg>