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.

examples/gallery/pages/buttons.rs

@@ -14,6 +14,7 @@ pub const PAGE: Page = Page {
     title: "Buttons & Actions",
     summary: "Seven variants, three sizes, one focus ring.",
     render,
+    script: &[],
 };
 
 const VARIANTS: [(ButtonVariant, &str); 7] = [