feat: isolate all four portals with route groups + polished design system

Fix blank /org/login (and /admin/login): the guarded portal layout was
wrapping its own login route, rendering null when unauthenticated. Move
each portal's authed pages into a (authed)/(chapter) route group so login
pages live outside the guard.

Structure:
- app/(chapter)/* — chapter admin pages + guarded layout (was root-level)
- app/org/(authed)/* — org pages + guarded layout; /org/login now free
- app/admin/(authed)/* — admin pages + guarded layout; /admin/login free
- Root layout slimmed to providers only (no shared sidebar)
- Convert moved files' relative imports to @/app alias

Design system:
- PortalShell: shared sidebar shell (brand mark, themed active nav with
  accent bar, avatar dropdown user menu, loading skeletons)
- portal-theme.ts: per-portal theme tokens (violet/slate/blue/emerald)
- PortalLoginShell redesigned: two-column with gradient branding panel,
  dotted pattern, value-prop highlights, built-in back link
- New shadcn components: Avatar, DropdownMenu, Skeleton
- Move shared DraftCard to _components/draft-card.tsx (used by 2 portals)
- Portal selector: remove Super Admin card, icon tiles, hover lift
- All 4 login pages use react-hook-form + Zod + themed shell
- Member nav restored to full 11-section list with icons

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/app/member-login/page.tsx

@@ -55,10 +55,11 @@ export default function MemberLoginPage() {
     <PortalLoginShell
       title="Member Portal"
       subtitle={step === 'phone' ? 'Enter your WhatsApp number to receive a sign-in code.' : `We sent a 6-digit code to ${phone} on WhatsApp.`}
-      accentClass="bg-emerald-600"
+      theme="emerald"
+      highlights={['Read your community digests', 'Manage privacy & consent', 'Discover events and members']}
       footer={
         step === 'phone'
-          ? <><Link href="/onboard" className="hover:text-foreground transition-colors">First time? Use your invite link</Link> · <Link href="/" className="hover:text-foreground transition-colors">Portal selector</Link></>
+          ? <Link href="/onboard" className="text-emerald-600 hover:underline">First time? Use your invite link</Link>
           : undefined
       }
     >