feat(landing): Astro-Landingpage für Cardecky

Neue statische Astro 5-App in apps/landing/ (Port 4380).
Sektionen: Nav, Hero, Kartentypen-Grid (6 Typen), How-it-works,
Features, mana-e.V.-Pitch, CTA, Footer.

Stack: Astro 5 + Tailwind 3, kein MDX (overkill für MVP), keine
externen Abhängigkeiten. Forest-grüne Farbpalette passend zum App-
Theme, Serif-Headings im mana-e.V.-Stil.

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

apps/landing/src/styles/base.css

@@ -0,0 +1,26 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+html {
+	scroll-behavior: smooth;
+	-webkit-font-smoothing: antialiased;
+}
+
+body {
+	overflow-x: hidden;
+	background-color: theme('colors.paper');
+	color: theme('colors.ink');
+}
+
+@layer components {
+	.btn-primary {
+		@apply inline-flex items-center gap-2 rounded-lg bg-leaf px-5 py-2.5 text-sm font-medium text-white transition-colors hover:bg-leaf-hover focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-leaf focus-visible:ring-offset-2;
+	}
+	.btn-ghost {
+		@apply inline-flex items-center gap-2 rounded-lg border border-rule px-5 py-2.5 text-sm font-medium text-ink transition-colors hover:border-muted hover:bg-rule focus-visible:outline-none;
+	}
+	.section-label {
+		@apply text-xs font-semibold uppercase tracking-widest text-leaf;
+	}
+}