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/probe.rs

@@ -0,0 +1,25 @@
+use std::collections::HashMap;
+
+use ely_gpui_component::primitives::Measure;
+use gpui::{App, Bounds, Global, IntoElement, ParentElement, Pixels};
+
+/// Window bounds of named demo elements, for scripted capture.
+#[derive(Default)]
+pub struct Probes(HashMap<&'static str, Bounds<Pixels>>);
+
+impl Global for Probes {}
+
+impl Probes {
+    pub fn get(key: &str, cx: &App) -> Option<Bounds<Pixels>> {
+        cx.try_global::<Probes>()
+            .and_then(|probes| probes.0.get(key).copied())
+    }
+}
+
+/// Wraps `element` so scripts can find it by `key`.
+pub fn probe(key: &'static str, element: impl IntoElement) -> Measure {
+    Measure::new(key, move |bounds, _, cx| {
+        cx.default_global::<Probes>().0.insert(key, bounds);
+    })
+    .child(element)
+}