Desktop OIDC: full page nav to localhost, meta redirect back

SPA navigates to 127.0.0.1:18901/oidc/start, passing ret URL.
Go opens browser, waits for callback, saves token, returns HTML with
<meta refresh> back to Wails app with ?desktop=1&token=TOKEN.
main.ts extracts token from URL on reload.

web/src/lib/oidc.ts

@@ -103,7 +103,9 @@ export async function startLogin(): Promise<void> {
 
   if (isDesktop) {
     const apiUrl = getConfig().apiUrl || ''
-    throw new Error('DESKTOP_OIDC:' + apiUrl)
+    const ret = encodeURIComponent(location.origin + location.pathname.replace(/\/$/, '') + '?desktop=1')
+    location.href = `http://127.0.0.1:18901/oidc/start?apiUrl=${encodeURIComponent(apiUrl)}&ret=${ret}`
+    return
   }
 
   location.href = `${cfg.authorization_endpoint.replace(/\/$/, '')}/?${params}`