feat: add Sheet and Sidebar components for improved UI layout

- Introduced a new Sheet component for modal-like functionality with customizable content and animations.
- Implemented a Sidebar component with mobile responsiveness, state management, and keyboard shortcuts for toggling.
- Added Skeleton component for loading states and Tooltip component for enhanced user guidance.
- Created a useIsMobile hook to manage mobile view detection.
- Updated main entry point to render the new PlatformPage component.
- Enhanced styles for sidebar and scrollbar customization in CSS.
- Extended Tailwind configuration to include sidebar color variables for better theming.

frontend/src/hooks/use-mobile.tsx

@@ -0,0 +1,19 @@
+import * as React from "react"
+
+const MOBILE_BREAKPOINT = 768
+
+export function useIsMobile() {
+  const [isMobile, setIsMobile] = React.useState<boolean | undefined>(undefined)
+
+  React.useEffect(() => {
+    const mql = window.matchMedia(`(max-width: ${MOBILE_BREAKPOINT - 1}px)`)
+    const onChange = () => {
+      setIsMobile(window.innerWidth < MOBILE_BREAKPOINT)
+    }
+    mql.addEventListener("change", onChange)
+    setIsMobile(window.innerWidth < MOBILE_BREAKPOINT)
+    return () => mql.removeEventListener("change", onChange)
+  }, [])
+
+  return !!isMobile
+}