feat(ux): shared PageTitle/SectionTitle primitive, adopt app-wide

- new components/ui/page-title.tsx (PageHeader/PageTitle/SectionTitle)
- every page heading routed through PageTitle (one source of truth
  for the page-title style; identical render)
- members restricted-directory screen now uses the standard
  PageHeader bar instead of an off-style mono heading

app/(app)/profile/page.tsx

@@ -2,6 +2,7 @@ import { redirect } from 'next/navigation'
 import { createClient } from '@/lib/supabase/server'
 import { ProfileForm } from './profile-form'
 import { AffiliationsForm } from './affiliations-form'
+import { PageTitle } from '@/components/ui/page-title'
 
 export const dynamic = 'force-dynamic'
 
@@ -39,7 +40,7 @@ export default async function ProfilePage() {
   return (
     <div className="min-h-screen bg-background">
       <div className="bg-sidebar px-4 md:px-6 py-3">
-        <h1 className="text-white font-sans text-lg font-semibold">My profile</h1>
+        <PageTitle>My profile</PageTitle>
       </div>
 
       <div className="p-4 md:p-6 space-y-6 max-w-3xl">