perf: add export loading state and virtual scrolling for large lists

Export modal now shows a loading indicator and doesn't freeze the UI.
Large list modals use virtual scrolling for smooth performance.

package-lock.json

@@ -14,6 +14,7 @@
         "@simplewebauthn/browser": "^13.2.2",
         "@stripe/react-stripe-js": "^5.6.0",
         "@stripe/stripe-js": "^8.7.0",
+        "@tanstack/react-virtual": "^3.13.21",
         "axios": "^1.13.2",
         "class-variance-authority": "^0.7.1",
         "cobe": "^0.6.5",
@@ -5405,6 +5406,33 @@
         "tailwindcss": ">=3.0.0 || insiders || >=4.0.0-alpha.20 || >=4.0.0-beta.1"
       }
     },
+    "node_modules/@tanstack/react-virtual": {
+      "version": "3.13.21",
+      "resolved": "https://registry.npmjs.org/@tanstack/react-virtual/-/react-virtual-3.13.21.tgz",
+      "integrity": "sha512-SYXFrmrbPgXBvf+HsOsKhFgqSe4M6B29VHOsX9Jih9TlNkNkDWx0hWMiMLUghMEzyUz772ndzdEeCEBx+3GIZw==",
+      "license": "MIT",
+      "dependencies": {
+        "@tanstack/virtual-core": "3.13.21"
+      },
+      "funding": {
+        "type": "github",
+        "url": "https://github.com/sponsors/tannerlinsley"
+      },
+      "peerDependencies": {
+        "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0",
+        "react-dom": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0"
+      }
+    },
+    "node_modules/@tanstack/virtual-core": {
+      "version": "3.13.21",
+      "resolved": "https://registry.npmjs.org/@tanstack/virtual-core/-/virtual-core-3.13.21.tgz",
+      "integrity": "sha512-ww+fmLHyCbPSf7JNbWZP3g7wl6SdNo3ah5Aiw+0e9FDErkVHLKprYUrwTm7dF646FtEkN/KkAKPYezxpmvOjxw==",
+      "license": "MIT",
+      "funding": {
+        "type": "github",
+        "url": "https://github.com/sponsors/tannerlinsley"
+      }
+    },
     "node_modules/@testing-library/dom": {
       "version": "10.4.1",
       "resolved": "https://registry.npmjs.org/@testing-library/dom/-/dom-10.4.1.tgz",