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/users.svg

@@ -0,0 +1,18 @@
+<!-- @license lucide-static v1.48.0 - ISC -->
+<svg
+  class="lucide lucide-users"
+  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="M16 21v-2a4 4 0 0 0-4-4H6a4 4 0 0 0-4 4v2" />
+  <path d="M16 3.128a4 4 0 0 1 0 7.744" />
+  <path d="M22 21v-2a4 4 0 0 0-3-3.87" />
+  <circle cx="9" cy="7" r="4" />
+</svg>