refactor(17-04): remove placeholder New Initiative button from AppLayout header

The dashboard page now owns the create action via its own header button
and empty state CTA. This keeps AppLayout generic — other pages like
Inbox shouldn't show initiative-specific actions.

packages/web/src/layouts/AppLayout.tsx

@@ -1,5 +1,4 @@
 import { Link } from '@tanstack/react-router'
-import { Button } from '@/components/ui/button'
 
 const navItems = [
   { label: 'Initiatives', to: '/initiatives', enabled: true },
@@ -18,9 +17,6 @@ export function AppLayout({ children }: { children: React.ReactNode }) {
           <Link to="/initiatives" className="text-lg font-bold tracking-tight">
             Codewalk District
           </Link>
-          <Button size="sm" onClick={() => { /* placeholder - Phase 17 */ }}>
-            + New Initiative
-          </Button>
         </div>
         {/* Navigation */}
         <nav className="mx-auto flex max-w-7xl gap-1 px-6 pb-2">