Build a single-file HTML landing page for a fictional mobile app called "람쥐썬더" (Ramjwi Thunder). The mascot is a lightning-fast cartoon squirrel: every to-do you finish becomes an acorn the squirrel stashes, and keeping a daily streak charges up a thunder bolt. Write all page copy in natural, witty Korean for Korean users in their 20s and 30s. Include: a hero section with a headline, a one-line pitch and a pair of App Store / Google Play style download buttons; an animated phone mockup showing the app's main screen; three feature sections; a three-step "how it works"; a pricing block with a free plan and a paid plan; an FAQ with four questions; and a footer. Do not include user reviews or testimonials. Draw the squirrel mascot and every image in code (inline SVG or CSS; no external images, use system fonts). Add tasteful scroll animations and a dark mode toggle. Make it look like a polished, real product site on both desktop and phone.