T01 primitives: image, divider, backdrop, focus, pressable, measure, tooltip

Ely-built primitives plus gallery demos for every chapter-one entry,
including gpui natives. The gallery now scripts real input by posting
NSEvents to its own queue and shoots each interaction in both modes.
Codex gpt-6-astra (max): three rounds; the last finding, a two-line
doc comment, was fixed after the three-review cap.

assets/icons/image-off.svg

@@ -0,0 +1,20 @@
+<!-- @license lucide-static v1.48.0 - ISC -->
+<svg
+  class="lucide lucide-image-off"
+  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"
+>
+  <line x1="2" x2="22" y1="2" y2="22" />
+  <path d="M10.41 10.41a2 2 0 1 1-2.83-2.83" />
+  <line x1="13.5" x2="6" y1="13.5" y2="21" />
+  <line x1="18" x2="21" y1="12" y2="15" />
+  <path d="M3.59 3.59A1.99 1.99 0 0 0 3 5v14a2 2 0 0 0 2 2h14c.55 0 1.052-.22 1.41-.59" />
+  <path d="M21 15V5a2 2 0 0 0-2-2H9" />
+</svg>