feat(ZEE-29): implement design system, dark mode, and JSON content management

- Add comprehensive design system with CSS variables, animations, and utility classes
- Implement dark mode with ThemeProvider (system preference + manual toggle)
- Create JSON-based content management system in src/content/
- Update all pages to use structured JSON content
- Add ThemeProvider component with theme toggle button
- Update Header with glass effect and animated mobile menu
- Update Footer with dark mode support
- Update documentation (README.md, CLAUDE.md, knowledge.md, proto/README.md)
- Sync with Linear (ZEE-29 completed)

proto/src/content/index.ts

@@ -0,0 +1,62 @@
+/**
+ * Content Loader - Centralized content management
+ * 
+ * This module provides type-safe access to all JSON content files.
+ * Content can be easily modified by editing the JSON files without code changes.
+ * 
+ * Usage:
+ * import { content, getPageContent } from '@/content'
+ * 
+ * // Access specific page content
+ * const aboutContent = content.pages.about
+ * 
+ * // Or use the helper function
+ * const servicesContent = getPageContent('services')
+ */
+
+import type {
+  SiteContent,
+  CommonContent,
+  HomePageContent,
+  AboutPageContent,
+  ServicesPageContent,
+  ContactPageContent
+} from './types'
+
+// Import JSON files
+import commonJson from './common.json'
+import homeJson from './pages/home.json'
+import aboutJson from './pages/about.json'
+import servicesJson from './pages/services.json'
+import contactJson from './pages/contact.json'
+
+// Type assertions for JSON imports
+const common: CommonContent = commonJson as CommonContent
+const home: HomePageContent = homeJson as HomePageContent
+const about: AboutPageContent = aboutJson as AboutPageContent
+const services: ServicesPageContent = servicesJson as ServicesPageContent
+const contact: ContactPageContent = contactJson as ContactPageContent
+
+// Combined content object
+export const content: SiteContent = {
+  common,
+  pages: {
+    home,
+    about,
+    services,
+    contact
+  }
+}
+
+// Helper function to get page content with type safety
+export function getPageContent<T extends keyof SiteContent['pages']>(
+  page: T
+): SiteContent['pages'][T] {
+  return content.pages[page]
+}
+
+// Export individual content for direct imports
+export { common, home, about, services, contact }
+
+// Re-export types
+export * from './types'