Remove ToDo-Karten product and its dedicated /todo-cards page

Product deleted from Payload (no orders referenced it), so its bespoke
page went with it — Navbar's WERKZEUGE_ROUTES and the sitemap no longer
list it. The blog's "3minuten" relatedProduct pointer and the homepage's
"ToDo-Karten" Werkzeuge card were cleared/removed in Payload directly
(no code change needed there — CMS content).

Also fixes a real bug found in the process: ProductBlocks.tsx's
AddToCartButton calls never passed productId, silently falling back to
its "todo-karten" default — every block-driven PDP's buy button (e.g.
"Die Pause.") was adding the wrong product to the cart.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013Eg6h91yngXmSnM51wxXM8

app/components/Navbar.tsx

@@ -63,7 +63,7 @@ function getNavLinks(singleActiveProduct: boolean) {
 // /der-eine and /tasse-die-pause (both bespoke product detail pages, same
 // "own route, not nested" shape as /todo-cards) added here for the same
 // reason (2026-08-25).
-const WERKZEUGE_ROUTES = ["/todo-cards", "/7-tage-klarheits-check", "/newsletter", "/der-eine", "/tasse-die-pause", "/lebensuhr", "/3x3-system"];
+const WERKZEUGE_ROUTES = ["/7-tage-klarheits-check", "/newsletter", "/der-eine", "/tasse-die-pause", "/lebensuhr", "/3x3-system"];
 
 function isNavLinkActive(href: string, pathname: string, activeSection: string): boolean {
   if (href === "#werkzeuge") {