Refactor App.tsx from god component to context-based architecture

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/contexts/theme-context.tsx

@@ -0,0 +1,19 @@
+import { createContext, type ReactNode, useContext } from "react";
+import { useTheme } from "../hooks/use-theme.js";
+
+type ThemeContextValue = ReturnType<typeof useTheme>;
+
+const ThemeContext = createContext<ThemeContextValue | null>(null);
+
+export function ThemeProvider({ children }: { children: ReactNode }) {
+	const value = useTheme();
+	return (
+		<ThemeContext.Provider value={value}>{children}</ThemeContext.Provider>
+	);
+}
+
+export function useThemeContext(): ThemeContextValue {
+	const ctx = useContext(ThemeContext);
+	if (!ctx) throw new Error("useThemeContext requires ThemeProvider");
+	return ctx;
+}