Initialize CMS application scaffold

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

ui/app/src/auth.tsx

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+import { createContext, useCallback, useContext, useEffect, useMemo, useState, type ReactNode } from 'react'
+import { requestSession, signInWithGoogle, signOut, type User } from './api'
+
+type AuthState = {
+  user: User | null
+  loading: boolean
+  error: string | null
+  signIn: () => Promise<void>
+  signOut: () => Promise<void>
+}
+
+const AuthContext = createContext<AuthState | undefined>(undefined)
+
+function getUser(result: { authenticated?: boolean; user?: User; token?: string; accessToken?: string; sessionToken?: string }) {
+  const token = result.token ?? result.accessToken ?? result.sessionToken
+  if (token) sessionStorage.setItem('cms.auth.token', token)
+  return result.authenticated === false ? null : result.user ?? (token ? {} : null)
+}
+
+export function AuthProvider({ children }: { children: ReactNode }) {
+  const [user, setUser] = useState<User | null>(null)
+  const [loading, setLoading] = useState(true)
+  const [error, setError] = useState<string | null>(null)
+
+  const refresh = useCallback(async () => {
+    try {
+      setError(null)
+      const session = await requestSession()
+      setUser(session ? getUser(session) : null)
+    } catch (err) {
+      setUser(null)
+      setError(err instanceof Error ? err.message : 'Unable to check your session.')
+    } finally {
+      setLoading(false)
+    }
+  }, [])
+
+  useEffect(() => { void refresh() }, [refresh])
+
+  const signIn = useCallback(async () => {
+    setError(null)
+    try {
+      const result = await signInWithGoogle()
+      setUser(getUser(result))
+    } catch (err) {
+      setError(err instanceof Error ? err.message : 'Sign-in failed.')
+    }
+  }, [])
+
+  const logOut = useCallback(async () => {
+    await signOut().catch(() => undefined)
+    sessionStorage.removeItem('cms.auth.token')
+    setUser(null)
+  }, [])
+
+  const value = useMemo(() => ({ user, loading, error, signIn, signOut: logOut }), [user, loading, error, signIn, logOut])
+  return <AuthContext.Provider value={value}>{children}</AuthContext.Provider>
+}
+
+export function useAuth() {
+  const context = useContext(AuthContext)
+  if (!context) throw new Error('useAuth must be used inside AuthProvider')
+  return context
+}