feat: per-theme accent + Activity WhatsApp(en)/GitHub cards, softer icon borders

- theme: store accent separately for light/dark (theme-core/controls)
- en contacts: WhatsApp card instead of VK (wa.me link)
- Activity: add GitHub card (logo webp) in both locales
- mp-card__image border uses --line to match card (less contrast)

public/css/main.css

@@ -3383,7 +3383,7 @@ html[data-theme="light"] .hero__portrait-shell {
   height: auto;
   object-fit: cover;
   object-position: center;
-  border: 1px solid color-mix(in srgb, var(--line) 84%, var(--text) 16%);
+  border: 1px solid var(--line);
   border-radius: calc(var(--radius-card) - 4px);
   box-sizing: border-box;
 }
@@ -4400,6 +4400,10 @@ html[data-radius="strong"] .skill-task-card__solution {
   --contact-brand: #0077ff;
 }
 
+.contact-card--brand-whatsapp {
+  --contact-brand: #25D366;
+}
+
 .contact-card--brand-ya {
   --contact-brand: #f8604a;
 }