Drop turtle, honor ?template= URL param, add warp easter egg

- Removed the cosmos turtle (CSS rules + auto-load probe + JS hook).
  Reduced-motion turtle branch removed too.
- ?template=editorial|swiss|cosmos URL param now wins over the value
  in data/links.json (and the cached localStorage fallback). Wired in
  both the pre-paint boot script and main() so deep links work
  without flashing the wrong template.
- New hidden easter egg: type the letters w-a-r-p anywhere on the
  page (no input focused) and the page reloads on the next template
  in the cycle editorial -> swiss -> cosmos -> editorial. The URL is
  updated with the new ?template= param so the override survives
  refresh and is shareable. A small "↯ <name>" toast pops up after
  the reload via sessionStorage handoff, fades after ~2.5s, respects
  prefers-reduced-motion.
- README documents both the URL param and the warp keyword.

assets/css/styles.css

@@ -696,3 +696,33 @@ body::before {
 }
 
 .sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0; }
+
+/* warp toast — surfaces the active template after the easter egg fires */
+.warp-toast {
+  position: fixed;
+  bottom: clamp(1.25rem, 3vw, 2.25rem);
+  left: 50%;
+  z-index: 1000;
+  display: inline-flex;
+  align-items: center;
+  gap: 0.6rem;
+  padding: 0.6rem 1.1rem;
+  background: var(--ink);
+  color: var(--paper);
+  font: 600 var(--fs-sm)/1 var(--mono);
+  text-transform: uppercase;
+  letter-spacing: 0.18em;
+  border-radius: 999px;
+  box-shadow: 0 12px 30px -16px rgba(0, 0, 0, 0.5);
+  opacity: 0;
+  transform: translate(-50%, 18px);
+  animation: warp-in 360ms cubic-bezier(0.22, 1, 0.36, 1) forwards;
+  pointer-events: none;
+}
+.warp-toast__arrow { color: var(--accent); font-size: 1.1em; }
+.warp-toast--out { animation: warp-out 600ms ease forwards; }
+@keyframes warp-in  { to { opacity: 1; transform: translate(-50%, 0); } }
+@keyframes warp-out { to { opacity: 0; transform: translate(-50%, 18px); } }
+@media (prefers-reduced-motion: reduce) {
+  .warp-toast { animation: none; opacity: 1; transform: translate(-50%, 0); }
+}