feat(ST-903): load active product in layout, replace cookie with DB lookup in solo

- layout.tsx: fetch active_product_id, resolve product, clear stale ref server-side
- NavBar: add activeProduct prop (rendering changes in ST-904)
- solo/page.tsx: redirect via user.active_product_id instead of lastProductId cookie
- proxy.ts: remove lastProductId cookie logic
- lib/cookies.ts: deleted (no longer used)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

proxy.ts

@@ -5,9 +5,6 @@ import { sessionOptions } from '@/lib/session'
 const protectedRoutes = ['/dashboard', '/products', '/todos', '/settings', '/solo']
 const authRoutes = ['/login', '/register']
 
-const SOLO_ROUTE = /^\/products\/([^/]+)\/solo$/
-const THIRTY_DAYS_SECONDS = 60 * 60 * 24 * 30
-
 export function proxy(request: NextRequest) {
   const path = request.nextUrl.pathname
   const isProtected = protectedRoutes.some(r => path.startsWith(r))
@@ -24,20 +21,7 @@ export function proxy(request: NextRequest) {
     return NextResponse.redirect(new URL('/dashboard', request.url))
   }
 
-  const response = NextResponse.next()
-
-  // Remember last visited product for /solo redirect
-  const soloMatch = path.match(SOLO_ROUTE)
-  if (soloMatch) {
-    response.cookies.set('lastProductId', soloMatch[1], {
-      httpOnly: true,
-      sameSite: 'lax',
-      maxAge: THIRTY_DAYS_SECONDS,
-      path: '/',
-    })
-  }
-
-  return response
+  return NextResponse.next()
 }
 
 export const config = {