Embed Wails runtime.js, serve it from custom asset handler

The SPA needs /wails/runtime.js for window.wails to be available.
Since we use a custom AssetOptions.Handler, Wails' internal routing
doesn't serve it. Embed the runtime and serve it explicitly.

cmd/desktop/main.go

@@ -31,6 +31,9 @@ var assets embed.FS
 //go:embed icon.png
 var iconPNG []byte
 
+//go:embed runtime.js
+var runtimeJS []byte
+
 const (
 	keyringService = "com.hubris.oikos-desktop"
 	keyringUser    = "oikos"
@@ -330,6 +333,13 @@ func newAssetHandler(cfg *OikosConfig) http.Handler {
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		path := r.URL.Path
+
+		if path == "/wails/runtime.js" {
+			w.Header().Set("Content-Type", "application/javascript")
+			w.Write(runtimeJS)
+			return
+		}
+
 		if path == "/" || path == "/index.html" {
 			data, err := fs.ReadFile(distFS, "index.html")
 			if err != nil {