Reorganize repository into monorepo structure

Restructured the project to support multiple frontend applications:
- Move web app to web/ directory
- Create pezkuwi-sdk-ui/ for Polkadot SDK clone (planned)
- Create mobile/ directory for mobile app development
- Add shared/ directory with common utilities, types, and blockchain code
- Update README.md with comprehensive documentation
- Remove obsolete DKSweb/ directory

This monorepo structure enables better code sharing and organized
development across web, mobile, and SDK UI projects.

web/src/hooks/use-mobile.tsx

@@ -0,0 +1,21 @@
+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;
+}