Switch social-share icons to Lucide v0.460.0; shrink avatar to 40x40

Lucide (https://lucide.dev) replaces the hand-rolled Tabler paths. Lucide
is more compact and consistent, and ships under the ISC license (more
permissive than Tabler's MIT and equally fine for plugin redistribution).

Lucide has no brand icons for Reddit/WhatsApp/Pinterest, so we use
generic substitutes that preserve the visual intent:
- reddit.svg   <- lucide 'share-2'  (community share metaphor)
- whatsapp.svg <- lucide 'message-circle'
- pinterest.svg<- lucide 'pin'

Avatar: shrunk to 40x40 per user testing — sizes above 41x41 were being
clipped inside the round border on this host.

assets/icons/twitter.svg

@@ -0,0 +1,15 @@
+<!-- @license lucide-static v0.460.0 - ISC -->
+<svg
+  class="lucide lucide-twitter"
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  viewBox="0 0 24 24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <path d="M22 4s-.7 2.1-2 3.4c1.6 10-9.4 17.3-18 11.6 2.2.1 4.4-.6 6-2C3 15.5.5 9.6 3 5c2.2 2.6 5.6 4.1 9 4-.9-4.2 4-6.6 7-3.8 1.1 0 3-1.2 3-1.2z" />
+</svg>