fix(web): force WebGL2 backend

Affected Chromium adapters fail after selecting WebGPU even when packed renderer paths are forced. Use WebGL2 for the web app and let device limits select renderer tiers.\n\nRefs #788

src/app/mod.rs

@@ -3723,6 +3723,7 @@ pub fn run_web() -> iced::Result {
     .subscription(OpenCADStudio::subscription)
     .title(|_state: &OpenCADStudio| "Open CAD Studio".to_string())
     .theme(|state: &OpenCADStudio| state.active_theme.clone())
+    .backend(iced::Backend::Hardware(iced::backend::Api::OpenGL))
     .font(iced_aw::ICED_AW_FONT_BYTES)
     .run()
 }