refactor: convert to bun workspaces monorepo

- Move web app into apps/web/
- Create packages/shared/ with shared types
- Create plugins/decky-vault/ scaffold
- Root package.json manages workspaces only

apps/web/app/(manage)/manage/page.tsx

@@ -0,0 +1,15 @@
+import { DashboardOverview } from "@/components/manage/dashboard-overview";
+
+export default function ManagePage() {
+  return (
+    <div className="space-y-6">
+      <div>
+        <h1 className="text-2xl font-bold">Dashboard</h1>
+        <p className="text-sm text-zinc-400">
+          Overview of DeckyVault statistics and moderation queue
+        </p>
+      </div>
+      <DashboardOverview />
+    </div>
+  );
+}