Add js web stuff to landing page + documentation

go/cmd/kjol-web/wasm/main_native.go

@@ -0,0 +1,9 @@
+//go:build !(js && wasm)
+
+// The wasm client entry point (main.go) builds only under GOOS=js GOARCH=wasm.
+// This native placeholder keeps the package buildable on the host so a plain
+// `go build ./...` succeeds; the real client is built by ./build (or the dev
+// server) with GOOS=js GOARCH=wasm.
+package main
+
+func main() {}