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/components/theme-provider.tsx

@@ -0,0 +1,69 @@
+"use client"
+
+import * as React from "react"
+import { createContext, useContext, useEffect, useState } from "react"
+import { ThemeProviderProps } from "next-themes/dist/types"
+
+type Theme = "dark" | "light" | "system"
+
+type ThemeContextType = {
+  theme: Theme
+  setTheme: (theme: Theme) => void
+}
+
+const ThemeContext = createContext<ThemeContextType | null>(null)
+
+export function ThemeProvider({
+  children,
+  defaultTheme = "system",
+  value: _value,
+  ...props
+}: ThemeProviderProps) {
+  const [theme, setTheme] = useState<Theme>(() => {
+    if (typeof window !== "undefined") {
+      const savedTheme = localStorage.getItem("theme")
+      return (savedTheme && (savedTheme === "dark" || savedTheme === "light" || savedTheme === "system")
+        ? savedTheme
+        : defaultTheme) as Theme
+    }
+    return defaultTheme as Theme
+  })
+
+  useEffect(() => {
+    const root = window.document.documentElement
+    root.classList.remove("light", "dark")
+
+    if (theme === "system") {
+      const systemTheme = window.matchMedia("(prefers-color-scheme: dark)")
+        .matches
+        ? "dark"
+        : "light"
+      root.classList.add(systemTheme)
+      return
+    }
+
+    root.classList.add(theme)
+  }, [theme])
+
+  const value: ThemeContextType = {
+    theme,
+    setTheme: (theme: Theme) => {
+      localStorage.setItem("theme", theme)
+      setTheme(theme)
+    },
+  }
+
+  return (
+    <ThemeContext.Provider value={value} {...props}>
+      {children}
+    </ThemeContext.Provider>
+  )
+}
+
+export const useTheme = (): ThemeContextType => {
+  const context = useContext(ThemeContext)
+  if (!context) {
+    throw new Error("useTheme must be used within a ThemeProvider")
+  }
+  return context
+}