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.

src/primitives/mod.rs

@@ -1,3 +1,17 @@
+mod backdrop;
+mod divider;
+mod focus;
 mod icon;
+mod image;
+mod measure;
+mod pressable;
+mod tooltip;
 
+pub use backdrop::Backdrop;
+pub use divider::Divider;
+pub use focus::{FocusNext, FocusPrev, FocusRing, FocusScope};
 pub use icon::{Icon, IconName};
+pub use image::Image;
+pub use measure::{IntersectionObserver, Measure};
+pub use pressable::Pressable;
+pub use tooltip::{Tooltip, TooltipTrigger};