Introduce focus mode to help users concentrate on tasks at hand

Implements FocusMode component with ambient sounds, distraction blocking and adds FocusPage.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: c5f0c281-8dd8-4846-b452-4a07bcd21062
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/9777c70b-fc38-4831-8d6b-78dfffe041b0/5abfa1d7-294e-4d88-a0a7-e2cbc6cee435.jpg

client/src/components/layout/Header.tsx

@@ -13,6 +13,7 @@ import {
   DropdownMenuTrigger,
 } from "@/components/ui/dropdown-menu";
 import { LanguageSwitcher } from "@/components/LanguageSwitcher";
+import FocusButton from "@/components/focus/FocusButton";
 import { 
   Moon, 
   Sun, 
@@ -82,6 +83,9 @@ export default function Header() {
           {/* Language Switcher */}
           <LanguageSwitcher />
 
+          {/* Focus Mode */}
+          {user && <FocusButton variant="ghost" size="sm" />}
+
           {/* Theme Toggle */}
           <Button
             variant="ghost"