T00 foundation: theme, motion, assets, icon, buttons, gallery

Theme tokens in light and dark with high contrast, a palette cross-fade,
motion curves and a damped spring, embedded Lucide icons with Inter and
JetBrains Mono, Icon, Button, IconButton, and a gallery that captures
its own window. Reviewed by codex gpt-6-astra (max): PASS in round 3.

assets/icons/save.svg

@@ -0,0 +1,17 @@
+<!-- @license lucide-static v1.48.0 - ISC -->
+<svg
+  class="lucide lucide-save"
+  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="M15.2 3a2 2 0 0 1 1.4.6l3.8 3.8a2 2 0 0 1 .6 1.4V19a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2z" />
+  <path d="M17 21v-7a1 1 0 0 0-1-1H8a1 1 0 0 0-1 1v7" />
+  <path d="M7 3v4a1 1 0 0 0 1 1h7" />
+</svg>