feat: age verification with an ID document (Didit), and closed registration

Age: a Didit provider behind the vendor-neutral age interface. A person
verifies once (ID document, passive liveness, face match) and all their
linked IMVU accounts count as adult. Webhooks are checked against Didit's
signatures; only "over 18" is kept. A later answer replaces an earlier one
(an approval taken back is revoked). Checks are limited: one unfinished
check per person, 3 in 30 days, none once verified, and a monthly cap
(DIDIT_MONTHLY_LIMIT, default 30: Didit's free plan is $10 of credit a
month and a check costs $0.30). The Account page gets an Age Verification
card.

Registration: open or closed, an admin's setting in the console
(default from REGISTRATION). Closed: new accounts can only sign in until
a moderator approves them (or declines, deleting the account); the
website shows them a waiting page and the API treats them as signed out.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/web/app/account/actions.ts

@@ -1,5 +1,6 @@
 "use server";
 import { revalidatePath } from "next/cache";
+import { redirect } from "next/navigation";
 import { api, unwrap } from "@/lib/api";
 import { attempt, field, type ActionState } from "@/lib/actions";
 
@@ -58,3 +59,15 @@ export async function signOutComputers(_: ActionState, _form: FormData): Promise
     return "Signed out everywhere.";
   });
 }
+
+/** Starts an age check with a provider that checks the person, and sends them to its page. */
+export async function startAgeCheck(_: ActionState, form: FormData): Promise<ActionState> {
+  let url: string | undefined;
+  const state = await attempt(async () => {
+    const started = unwrap(await api.age({ provider: field(form, "provider") }).start.post({ returnURL: "/account?age=back" }));
+    if (started.kind === "redirect") url = started.url;
+    done();
+  });
+  if (url) redirect(url);
+  return state;
+}