T25a Generative: prompt and settings

PromptEnhancer offers a fuller prompt with the words it adds washed,
split at punctuation; Use this takes it into the field, Keep mine
lets it go. StylePresetPicker and AspectRatioPicker are rows of Tab
stops, the chosen one in accent; a ratio chip draws its shape.
SeedInput keeps digits up to u32::MAX and rolls one with a die.
NegativePromptInput and ImageGenerationPanel point to forms::TagInput
and forms::Form. theme.generative() holds the chapter's sizes. The
gallery's preset pictures are the atrium photo in five styles.

examples/gallery/pages/generative/mod.rs

@@ -0,0 +1,26 @@
+mod panel;
+
+use gpui::{AnyElement, App, IntoElement, ParentElement, Window, div};
+
+use super::Page;
+use crate::script::Step;
+
+pub const PAGE: Page = Page {
+    number: 25,
+    slug: "generative",
+    title: "Generative",
+    summary: "Making pictures, sound and video with a model: the prompt and its settings, the queue and what comes back, the canvas, and the models behind them.",
+    render,
+    script: SCRIPT,
+};
+
+const SCRIPT: &[Step] = &[
+    Step::DownAt("gen-enhancer", 356.0, 124.0),
+    Step::UpAt("gen-enhancer", 356.0, 124.0),
+    Step::Wait(1400),
+    Step::Shot("suggested"),
+];
+
+fn render(window: &mut Window, cx: &mut App) -> AnyElement {
+    div().child(panel::panel(window, cx)).into_any_element()
+}