docs: update documentation for v0.4.0 release

- Update README.md with v0.4.0 features and screenshots placeholders
- Update architecture.md with v0.4.0 implementation status
- Update progress.md marking all 27 tasks as completed
- Create CHANGELOG.md with complete release notes
- Add v0.4.0 frontend components and hooks

frontend/src/hooks/useTheme.ts

@@ -0,0 +1,10 @@
+import { useContext } from 'react';
+import { ThemeContext } from '@/providers/theme-context';
+
+export function useTheme() {
+  const context = useContext(ThemeContext);
+  if (context === undefined) {
+    throw new Error('useTheme must be used within a ThemeProvider');
+  }
+  return context;
+}