T44d Web · Gallery builds for wasm32: one story per section by URL, themed by the host

The gallery's entry runs natively or, on wasm32, from a wasm_bindgen start
through gpui_web, single-threaded with WebGL2 fallback. ?page, ?story and
?theme choose what shows; an unknown one fails in the page and the log.
set_theme switches the mode later. Pictures load from ELY_GALLERY_ASSETS.
scripts/stories.py writes examples/gallery/stories.json from the pages.

examples/gallery/pages/chat/compose.rs

@@ -1,5 +1,3 @@
-use std::time::Instant;
-
 use ely_gpui_component::{
     buttons::SegmentedControl,
     chat::{
@@ -13,6 +11,7 @@ use ely_gpui_component::{
     primitives::IconName,
 };
 use gpui::{App, Entity, IntoElement, ParentElement, SharedString, Styled, Window, div, px};
+use web_time::Instant;
 
 use crate::{
     probe::probe,