Add ToDo-Karten product page, fluid design tokens, and Navbar/Hero fixes

New /todo-cards page (Hero, How-it-works, Focus, Testimonials, Pricing)
built with the fluid clamp() token system (app/lib/fluid.ts) and
scroll-reveal animations (app/components/Reveal.tsx), matching styling
consistency with /challenge's testimonial section.

Navbar: page-aware active state and anchor-link navigation from any
route (not just "/"), fixed logo click to actually navigate instead of
silently rewriting the URL, fluid nav text size, custom hash-scroll
handling for cross-page anchor links.

Hero: responsive breakpoint fix for the text/image split at Tablet
widths, entrance animation for the brand's orange dot, removed a red
dot artifact from hero.png.

Also includes prior uncommitted work on About/Blog/Newsletter/Footer
and the cart lib (app/lib/cart.ts).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

public/icon-lock.svg

@@ -0,0 +1,6 @@
+<svg preserveAspectRatio="none" width="100%" height="100%" overflow="visible" style="display: block;" viewBox="0 0 14 14" fill="none" xmlns="http://www.w3.org/2000/svg">
+<g id="icon-lock">
+<path id="Vector" d="M10.3 6H3.7C3.03726 6 2.5 6.53726 2.5 7.2V10.8C2.5 11.4627 3.03726 12 3.7 12H10.3C10.9627 12 11.5 11.4627 11.5 10.8V7.2C11.5 6.53726 10.9627 6 10.3 6Z" stroke="var(--stroke-0, #222221)" stroke-width="1.2"/>
+<path id="Vector_2" d="M4.5 6V4.3C4.5 2.98 5.57 1.9 6.9 1.9H7.1C8.43 1.9 9.5 2.98 9.5 4.3V6" stroke="var(--stroke-0, #222221)" stroke-width="1.2" stroke-linecap="round"/>
+</g>
+</svg>