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>

app/lib/fluid.ts

@@ -0,0 +1,18 @@
+const MIN_VW = 768;
+const MAX_VW = 1440;
+
+/**
+ * Fluid clamp() between two px values, scaling with viewport width from
+ * `minVw` to `maxVw`. Below `minVw` the clamp() floor freezes the value —
+ * that's the "Tablet-Floor" behavior baked into the formula itself, no
+ * separate mobile media query needed for sizing.
+ */
+export function fluid(minPx: number, maxPx: number, minVw = MIN_VW, maxVw = MAX_VW): string {
+  const slope = (maxPx - minPx) / (maxVw - minVw);
+  const yIntercept = minPx - slope * minVw;
+  const minRem = minPx / 16;
+  const maxRem = maxPx / 16;
+  const yRem = yIntercept / 16;
+  const slopeVw = slope * 100;
+  return `clamp(${minRem}rem, ${yRem}rem + ${slopeVw}vw, ${maxRem}rem)`;
+}