fix(api,frontend): delete is the true inverse of adopt, no reseed

/creatures/:id/delete now just removes the row, matching how
POST /creatures (adopt) just inserts one — no side effects on anything
else. The auto-reseed was scope creep for a feature that only ever made
sense as a public marketing-site action; now that delete lives in the app
itself as a per-creature control, that safety net isn't needed.

Adds a Delete button next to Feed/Play/Sleep/Revive on every creature
card, same creatureAction() plumbing as the existing actions.

frontend/style.css

@@ -295,6 +295,14 @@ body::before {
   color: var(--accent-green);
 }
 
+.action-btn.delete {
+  background: rgba(255, 68, 102, 0.1);
+  border-color: rgba(255, 68, 102, 0.2);
+  color: var(--accent-red);
+  flex: 0 0 auto;
+  width: 44px;
+}
+
 /* ---- FAB ---- */
 .fab {
   position: fixed;