feat: add profile fields for local users

DB→domain→API→AP→frontend end-to-end. Fields stored as
JSONB, exposed via PATCH /users/me, serialized as AP
PropertyValue attachment. Editor in federation settings,
display on profile card.

thoughts-frontend/app/settings/federation/page.tsx

@@ -1,7 +1,9 @@
 import { cookies } from "next/headers";
 import { redirect } from "next/navigation";
+import { getMe } from "@/lib/api";
 import { FederationPanel } from "@/components/federation/federation-panel";
 import { MigrationSettings } from "@/components/federation/migration-settings";
+import { ProfileFieldsEditor } from "@/components/profile-fields-editor";
 
 export default async function FederationSettingsPage() {
   const token = (await cookies()).get("auth_token")?.value;
@@ -9,6 +11,8 @@ export default async function FederationSettingsPage() {
     redirect("/login");
   }
 
+  const me = await getMe(token);
+
   return (
     <div className="space-y-6">
       <div className="glass-effect glossy-effect bottom rounded-md shadow-fa-lg p-4">
@@ -18,6 +22,7 @@ export default async function FederationSettingsPage() {
           other instances.
         </p>
       </div>
+      <ProfileFieldsEditor initial={me.profileFields} />
       <FederationPanel />
       <MigrationSettings />
     </div>