fix: rework setup to improve SSR compatibility

composables/injections.ts

@@ -0,0 +1,14 @@
+import { InjectionKeyColorMode, InjectionKeyFontSize } from '~/constants/symbols'
+
+export function useFontSizeRef() {
+  return inject(InjectionKeyFontSize)!
+}
+
+export function useColorModeRef() {
+  return inject(InjectionKeyColorMode)!
+}
+
+export function toggleColorMode() {
+  const colorMode = useColorModeRef()
+  colorMode.value = colorMode.value === 'light' ? 'dark' : 'light'
+}