feat: restructure styles and components for improved design system

- Added typography and design system styles to globals.css.
- Removed deprecated home.css and landing.css files.
- Introduced DiscordSignInButton component for Discord authentication.
- Created Card and CardGrid components for structured content display.
- Implemented ContainerShowcase to demonstrate card usage and layout.
- Added DesignSystemTabs for navigation between design system sections.
- Established typography.css for consistent text styling across components.
- Added tests for typography styles to ensure compliance with design standards.

src/components/design-system/CalendarHeatmap.tsx

@@ -32,7 +32,7 @@ export function CalendarHeatmap({
   historyLabel?: string;
   legend?: ReactNode;
 }) {
-  const [months, setMonths] = useState<MonthView>(6);
+  const [months, setMonths] = useState<MonthView>(12);
   const latestDate =
     allDays.findLast((day) => day.state !== "future")?.date ??
     allDays.at(-1)?.date;