add shared login pin mechansim

frontend/src/routes/login/+page.server.ts

@@ -1,6 +1,6 @@
 import { fail, redirect } from '@sveltejs/kit';
 import { createPbClient } from '$lib/server/pocketbase';
-import { setSessionCookie } from '$lib/server/session';
+import { setSessionCookie, clearActiveChild } from '$lib/server/session';
 import { pbAdmin } from '$lib/server/pocketbase';
 import { handleOf } from '@shared/slugify';
 
@@ -27,6 +27,8 @@ export const actions = {
 		}
 
 		setSessionCookie(event.cookies, authResult.token);
+		// An explicit email/password login supersedes kid mode on a shared device.
+		clearActiveChild(event.cookies);
 
 		const fam = await pbAdmin.getOne('fams', user.famId).catch(() => null);
 		const famSlug = fam?.slug || user.famId;