Default to dark mode, add FOUC-prevention script

Change default theme from `system` to `dark`. Add inline `<script>` in
`index.html` that reads `localStorage` and sets `data-theme` before
React hydrates, preventing flash of wrong theme on load. Also update
theme cycle order to dark → light → system.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ryan-williams

www/index.html

@@ -5,6 +5,15 @@
     <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <link rel="stylesheet" href="node_modules/@fortawesome/fontawesome-free/css/all.min.css" />
+    <script>
+      (function() {
+        var mode = localStorage.getItem('awair-theme') || 'dark'
+        var theme = mode
+        if (mode === 'system')
+          theme = window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
+        document.documentElement.setAttribute('data-theme', theme)
+      })()
+    </script>
     <title>Awair Dashboard</title>
 
     <!-- OpenGraph tags -->

www/src/App.tsx

@@ -216,7 +216,7 @@ function AppContent() {
                 key: 'theme',
                 label: `Theme: ${theme === 'light' ? 'Light' : theme === 'dark' ? 'Dark' : 'System'}`,
                 icon: theme === 'light' ? <MdLightMode /> : theme === 'dark' ? <MdDarkMode /> : <MdBrightnessAuto />,
-                onClick: () => setTheme(theme === 'light' ? 'dark' : theme === 'dark' ? 'system' : 'light'),
+                onClick: () => setTheme(theme === 'dark' ? 'light' : theme === 'light' ? 'system' : 'dark'),
               },
             ]} />
             <ShortcutsModal

www/src/contexts/ThemeContext.tsx

@@ -13,7 +13,7 @@ const ThemeContext = createContext<ThemeContextType | undefined>(undefined)
 export function ThemeProvider({ children }: { children: ReactNode }) {
   const [theme, setTheme] = useState<Theme>(() => {
     const stored = localStorage.getItem('awair-theme')
-    return (stored as Theme) || 'system'
+    return (stored as Theme) || 'dark'
   })
 
   const [systemTheme, setSystemTheme] = useState<'light' | 'dark'>(() => {