feat: replace settings page with SettingsModal

- Add SettingsModalProvider context and SettingsModalWrapper
- Wire Header onOpenSettings callback via LayoutInner pattern
- Remove old /settings page and SettingsPageClient
- Bump @ciphera-net/ui to ^0.0.88

lib/settings-modal-context.tsx

@@ -0,0 +1,31 @@
+'use client'
+
+import { createContext, useContext, useState, useCallback } from 'react'
+
+interface SettingsModalContextType {
+  isOpen: boolean
+  openSettings: () => void
+  closeSettings: () => void
+}
+
+const SettingsModalContext = createContext<SettingsModalContextType>({
+  isOpen: false,
+  openSettings: () => {},
+  closeSettings: () => {},
+})
+
+export function SettingsModalProvider({ children }: { children: React.ReactNode }) {
+  const [isOpen, setIsOpen] = useState(false)
+  const openSettings = useCallback(() => setIsOpen(true), [])
+  const closeSettings = useCallback(() => setIsOpen(false), [])
+
+  return (
+    <SettingsModalContext.Provider value={{ isOpen, openSettings, closeSettings }}>
+      {children}
+    </SettingsModalContext.Provider>
+  )
+}
+
+export function useSettingsModal() {
+  return useContext(SettingsModalContext)
+}