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/_components/ui/avatar.tsx

@@ -0,0 +1,39 @@
+'use client';
+
+import * as React from 'react';
+import * as AvatarPrimitive from '@radix-ui/react-avatar';
+import { cn } from '@/app/_lib/utils';
+
+const Avatar = React.forwardRef<
+  React.ComponentRef<typeof AvatarPrimitive.Root>,
+  React.ComponentPropsWithoutRef<typeof AvatarPrimitive.Root>
+>(({ className, ...props }, ref) => (
+  <AvatarPrimitive.Root
+    ref={ref}
+    className={cn('relative flex size-9 shrink-0 overflow-hidden rounded-full', className)}
+    {...props}
+  />
+));
+Avatar.displayName = AvatarPrimitive.Root.displayName;
+
+const AvatarImage = React.forwardRef<
+  React.ComponentRef<typeof AvatarPrimitive.Image>,
+  React.ComponentPropsWithoutRef<typeof AvatarPrimitive.Image>
+>(({ className, ...props }, ref) => (
+  <AvatarPrimitive.Image ref={ref} className={cn('aspect-square h-full w-full', className)} {...props} />
+));
+AvatarImage.displayName = AvatarPrimitive.Image.displayName;
+
+const AvatarFallback = React.forwardRef<
+  React.ComponentRef<typeof AvatarPrimitive.Fallback>,
+  React.ComponentPropsWithoutRef<typeof AvatarPrimitive.Fallback>
+>(({ className, ...props }, ref) => (
+  <AvatarPrimitive.Fallback
+    ref={ref}
+    className={cn('flex h-full w-full items-center justify-center rounded-full bg-muted text-xs font-medium', className)}
+    {...props}
+  />
+));
+AvatarFallback.displayName = AvatarPrimitive.Fallback.displayName;
+
+export { Avatar, AvatarImage, AvatarFallback };