feat(web): copyable on-page banner for renderer errors (#414)

wgpu/naga report pipeline and shader failures through the log facade,
then leave the canvas empty - with no logger installed on wasm the
message was lost, so a broken GPU path looked like "draws nothing" with
a clean console. Install a web logger that mirrors Error-level records
to the browser console and into a fixed DOM overlay with selectable
text, a Copy button and repeat-collapsing; panics land in the same
banner via a chained hook. Windows Chrome/Edge reporters can now paste
the exact ANGLE/D3D11 error instead of a screenshot of a blank canvas.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/main.rs

@@ -28,6 +28,11 @@ fn main() -> iced::Result {
     #[cfg(target_arch = "wasm32")]
     {
         console_error_panic_hook::set_once();
+        // After the console hook so the chained panic mirror keeps it; also
+        // installs the log-facade listener that surfaces wgpu/naga errors as
+        // a copyable on-page banner (#414 — an empty canvas otherwise gives
+        // reporters nothing to paste).
+        sys::web_diag::init();
         return app::run_web();
     }
     #[cfg(not(target_arch = "wasm32"))]