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.

Cargo.lock

@@ -1659,11 +1659,13 @@ dependencies = [
  "futures",
  "gpui",
  "gpui_platform",
+ "gpui_web",
  "image",
  "iso_currency",
  "isocountry",
  "isolang",
  "jiff",
+ "js-sys",
  "log",
  "objc",
  "pulldown-cmark",
@@ -1679,6 +1681,8 @@ dependencies = [
  "smallvec",
  "unicode-segmentation",
  "vte",
+ "wasm-bindgen",
+ "web-sys",
  "web-time",
  "wry",
 ]