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/portal-theme.ts

@@ -0,0 +1,58 @@
+export type PortalTheme = 'violet' | 'slate' | 'blue' | 'emerald';
+
+interface ThemeTokens {
+  /** Gradient for the logo mark and login branding panel */
+  gradient: string;
+  /** Text accent for the brand wordmark */
+  text: string;
+  /** Active nav item background */
+  activeBg: string;
+  /** Active nav item text */
+  activeText: string;
+  /** Active left indicator bar */
+  bar: string;
+  /** Ring/border tint used in login branding */
+  soft: string;
+}
+
+export const PORTAL_THEMES: Record<PortalTheme, ThemeTokens> = {
+  violet: {
+    gradient: 'bg-gradient-to-br from-violet-500 to-purple-700',
+    text: 'text-violet-600',
+    activeBg: 'bg-violet-50',
+    activeText: 'text-violet-700',
+    bar: 'bg-violet-600',
+    soft: 'text-violet-100',
+  },
+  slate: {
+    gradient: 'bg-gradient-to-br from-slate-700 to-slate-900',
+    text: 'text-slate-800',
+    activeBg: 'bg-slate-100',
+    activeText: 'text-slate-900',
+    bar: 'bg-slate-800',
+    soft: 'text-slate-200',
+  },
+  blue: {
+    gradient: 'bg-gradient-to-br from-blue-500 to-indigo-700',
+    text: 'text-blue-600',
+    activeBg: 'bg-blue-50',
+    activeText: 'text-blue-700',
+    bar: 'bg-blue-600',
+    soft: 'text-blue-100',
+  },
+  emerald: {
+    gradient: 'bg-gradient-to-br from-emerald-500 to-teal-700',
+    text: 'text-emerald-600',
+    activeBg: 'bg-emerald-50',
+    activeText: 'text-emerald-700',
+    bar: 'bg-emerald-600',
+    soft: 'text-emerald-100',
+  },
+};
+
+export function initials(name?: string | null, email?: string | null): string {
+  const source = (name ?? email ?? '?').trim();
+  const parts = source.split(/\s+/).filter(Boolean);
+  if (parts.length >= 2) return (parts[0][0] + parts[1][0]).toUpperCase();
+  return source.slice(0, 2).toUpperCase();
+}