feat(web): add SEO landing page

Trunk.toml

@@ -7,7 +7,10 @@
 #           cargo install trunk wasm-bindgen-cli
 
 [build]
-target = "index.html"
+target = "web-app.html"
+dist = "dist/app"
+public_url = "/app/"
+html_output = "index.html"
 # The crate has no Cargo features: the geometry kernel is pure Rust and
 # cross-compiles to wasm, so the web build gets the same solid modelling the
 # native one does.