fix(desktop): session persistence — refresh/login/context/empty-content 4-bug fix

1. App.tsx: add restoreSession() call on startup to prevent redirect
   to login page after refresh (isRestoring guard + BootstrapScreen)
2. CloneManager: call syncAgents() after loadClones() to restore
   currentAgent and conversation history on app load
3. zclaw-memory: add get_or_create_session() so frontend session UUID
   is persisted directly — kernel no longer creates mismatched IDs
4. openai.rs: assistant message content must be non-empty for
   Kimi/Qwen APIs — replace empty content with meaningful placeholders

Also includes admin-v2 ModelServices unified page (merge providers +
models + API keys into expandable row layout)

admin-v2/src/stores/themeStore.ts

@@ -0,0 +1,56 @@
+import { create } from 'zustand'
+
+type ThemeMode = 'light' | 'dark' | 'system'
+
+interface ThemeState {
+  mode: ThemeMode
+  resolved: 'light' | 'dark'
+}
+
+function getSystemTheme(): 'light' | 'dark' {
+  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
+}
+
+function resolveTheme(mode: ThemeMode): 'light' | 'dark' {
+  return mode === 'system' ? getSystemTheme() : mode
+}
+
+function applyTheme(resolved: 'light' | 'dark') {
+  const html = document.documentElement
+  html.classList.toggle('dark', resolved === 'dark')
+  html.setAttribute('data-theme', resolved)
+}
+
+function getInitialMode(): ThemeMode {
+  const stored = localStorage.getItem('zclaw_admin_theme')
+  if (stored === 'light' || stored === 'dark' || stored === 'system') return stored
+  return 'system'
+}
+
+const initialMode = getInitialMode()
+const initialResolved = resolveTheme(initialMode)
+applyTheme(initialResolved)
+
+export const useThemeStore = create<ThemeState>(() => ({
+  mode: initialMode,
+  resolved: initialResolved,
+}))
+
+export function setThemeMode(mode: ThemeMode) {
+  const resolved = resolveTheme(mode)
+  localStorage.setItem('zclaw_admin_theme', mode)
+  applyTheme(resolved)
+  useThemeStore.setState({ mode, resolved })
+}
+
+// Listen for system theme changes
+if (typeof window !== 'undefined') {
+  window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
+    const { mode } = useThemeStore.getState()
+    if (mode === 'system') {
+      const resolved = getSystemTheme()
+      applyTheme(resolved)
+      useThemeStore.setState({ resolved })
+    }
+  })
+}