feat: Rebuild admin-ui with Preact + Signals

Complete rebuild of the admin-ui using Preact + Signals for a lightweight,
reactive framework. Features include:

- Team-centric workdesks (UI, UX, QA, Admin)
- Comprehensive API client with 150+ DSS backend endpoints
- Dark mode with system preference detection
- Keyboard shortcuts and command palette
- AI chat sidebar with Claude integration
- Toast notifications system
- Export/import functionality for project backup
- TypeScript throughout with full type coverage

Bundle size: ~66KB main (21KB gzipped), ~5KB framework overhead

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

admin-ui/src/state/user.ts

@@ -0,0 +1,81 @@
+import { signal, computed } from '@preact/signals';
+
+// Types
+export interface UserPreferences {
+  theme: 'light' | 'dark' | 'auto';
+  sidebarCollapsed: boolean;
+  panelHeight: number;
+  defaultTeam: string;
+  keyboardShortcutsEnabled: boolean;
+  notificationsEnabled: boolean;
+}
+
+export interface User {
+  id: string;
+  name: string;
+  email: string;
+  avatar?: string;
+  role: 'admin' | 'developer' | 'viewer';
+}
+
+// Default preferences
+const DEFAULT_PREFERENCES: UserPreferences = {
+  theme: 'auto',
+  sidebarCollapsed: false,
+  panelHeight: 280,
+  defaultTeam: 'ui',
+  keyboardShortcutsEnabled: true,
+  notificationsEnabled: true
+};
+
+// User State Signals
+export const user = signal<User | null>(null);
+export const preferences = signal<UserPreferences>(DEFAULT_PREFERENCES);
+
+// Computed Values
+export const isAuthenticated = computed(() => user.value !== null);
+export const isAdmin = computed(() => user.value?.role === 'admin');
+export const userName = computed(() => user.value?.name ?? 'Guest');
+export const userInitials = computed(() => {
+  const name = user.value?.name ?? 'Guest';
+  return name.split(' ').map(n => n[0]).join('').toUpperCase().slice(0, 2);
+});
+
+// Actions
+export function loadUserPreferences(): void {
+  if (typeof window === 'undefined') return;
+
+  const saved = localStorage.getItem('dss-preferences');
+  if (saved) {
+    try {
+      const parsed = JSON.parse(saved);
+      preferences.value = { ...DEFAULT_PREFERENCES, ...parsed };
+    } catch {
+      preferences.value = DEFAULT_PREFERENCES;
+    }
+  }
+}
+
+export function saveUserPreferences(): void {
+  if (typeof window === 'undefined') return;
+  localStorage.setItem('dss-preferences', JSON.stringify(preferences.value));
+}
+
+export function updatePreferences(updates: Partial<UserPreferences>): void {
+  preferences.value = { ...preferences.value, ...updates };
+  saveUserPreferences();
+}
+
+export function setUser(userData: User | null): void {
+  user.value = userData;
+}
+
+export function logout(): void {
+  user.value = null;
+  localStorage.removeItem('dss-token');
+}
+
+// Keyboard shortcuts state
+export const keyboardShortcutsEnabled = computed(() =>
+  preferences.value.keyboardShortcutsEnabled
+);