chore: import upstream snapshot with attribution

apps/sim/lib/core/utils/theme.ts

@@ -0,0 +1,43 @@
+/**
+ * Theme synchronization utilities for managing theme across next-themes and database
+ */
+
+/**
+ * Updates the theme in next-themes by dispatching a storage event.
+ * This works by updating localStorage and notifying next-themes of the change.
+ * @param theme - The desired theme ('system', 'light', or 'dark')
+ */
+export function syncThemeToNextThemes(theme: 'system' | 'light' | 'dark') {
+  if (typeof window === 'undefined') return
+
+  const oldValue = localStorage.getItem('sim-theme')
+  localStorage.setItem('sim-theme', theme)
+
+  window.dispatchEvent(
+    new StorageEvent('storage', {
+      key: 'sim-theme',
+      newValue: theme,
+      oldValue: oldValue,
+      storageArea: localStorage,
+      url: window.location.href,
+    })
+  )
+
+  const root = document.documentElement
+  root.classList.remove('light', 'dark')
+
+  if (theme === 'system') {
+    const systemTheme = window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
+    root.classList.add(systemTheme)
+  } else {
+    root.classList.add(theme)
+  }
+}
+
+/**
+ * Gets the current theme from next-themes localStorage
+ */
+export function getThemeFromNextThemes(): 'system' | 'light' | 'dark' {
+  if (typeof window === 'undefined') return 'system'
+  return (localStorage.getItem('sim-theme') as 'system' | 'light' | 'dark') || 'system'
+}