Add import/export, graph UX improvements, and contact management fixes.

Support vCard import and multi-format export, bulk delete with reliable local persistence, Ctrl+link relation creation, cluster-colored graph visualization, and right-click context menus for node details.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/lib/uuid.js

@@ -0,0 +1,10 @@
+export function generateId() {
+  if (typeof crypto !== 'undefined' && typeof crypto.randomUUID === 'function') {
+    return crypto.randomUUID()
+  }
+  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, (c) => {
+    const r = (Math.random() * 16) | 0
+    const v = c === 'x' ? r : (r & 0x3) | 0x8
+    return v.toString(16)
+  })
+}