feat(site): human-language 'what you can do' features section

Add a features section to the landing home (EN/ES) that describes what
Tane does by intent, not mechanism: inventory, care & calendar, labels &
backup, and the neighbourly sharing layer (offers, chat, trust, plantaré,
sync). Follows the existing pillars/values pattern (front-matter data +
template + CSS, RTL-safe). Reframe the beta status copy so the sharing
layer reads as 'arriving, in beta' rather than 'being built'.

site/layouts/index.html

@@ -37,6 +37,24 @@
   {{ end }}
 </section>
 
+{{ with .Params.features }}
+<section class="features">
+  <h2>{{ .title }}</h2>
+  {{ with .intro }}<p class="features-intro">{{ . }}</p>{{ end }}
+  <div class="feature-groups">
+    {{ range .groups }}
+    <article class="feature-group">
+      <div class="feature-icon" aria-hidden="true">{{ .icon }}</div>
+      <h3>{{ .title }}</h3>
+      <ul>
+        {{ range .items }}<li>{{ . }}</li>{{ end }}
+      </ul>
+    </article>
+    {{ end }}
+  </div>
+</section>
+{{ end }}
+
 {{ $screens := slice "home" "inventory" "market" "calendar" "detail" }}
 <section class="shots">
   <h2>{{ T "screenshotsTitle" }}</h2>