feat(#48): Add dark mode

src/lib/stores/theme.ts

@@ -0,0 +1,37 @@
+import { writable } from 'svelte/store';
+
+type Theme = 'pokeball' | 'dark';
+
+const STORAGE_KEY = 'theme';
+
+function createThemeStore() {
+	// Get stored theme from localStorage or default to 'pokeball'
+	const storedTheme = (typeof window !== 'undefined' &&
+		localStorage.getItem(STORAGE_KEY)) as Theme | null;
+	const initialTheme: Theme = storedTheme || 'pokeball';
+
+	const { subscribe, set, update } = writable<Theme>(initialTheme);
+
+	return {
+		subscribe,
+		set,
+		toggle: () => update((theme) => (theme === 'pokeball' ? 'dark' : 'pokeball')),
+		init: () => {
+			if (typeof window !== 'undefined') {
+				const stored = localStorage.getItem(STORAGE_KEY) as Theme | null;
+				if (stored) {
+					set(stored);
+				}
+			}
+		}
+	};
+}
+
+export const theme = createThemeStore();
+
+// Helper function to apply theme to HTML element
+export function applyTheme(themeValue: Theme) {
+	if (typeof document !== 'undefined') {
+		document.documentElement.setAttribute('data-theme', themeValue);
+	}
+}