fix(dev): serve the HMR client as an external script

A document's CSP nonce is fixed at load, so an inline script delivered by
a later response can never carry a nonce that document accepts. The HMR
client is now served at /__wrnexus/hmr-client.js, which script-src 'self'
already covers and which needs no nonce at all.

This removes one of the two inline scripts CSP was blocking in
development. The i18n data script is still blocked and needs the same
treatment; it is shared with the CSR navigation and HMR parsers, so
moving it spans @wrnexus/i18n, csr, and dev-server.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/dev-server/src/assets.ts

@@ -34,6 +34,7 @@ import type { AssetServer } from "./runtime.ts";
 import { servePublicAsset } from "./public.ts";
 import { servePluginAsset, type ServedPluginAsset } from "./plugin-assets.ts";
 import { serveIslandArtifact, serveWrnBrowserArtifact } from "./pipeline.ts";
+import { HMR_CLIENT_HREF, HMR_CLIENT_JS } from "./runtime.ts";
 
 /** Style inputs the dev asset server needs to build `/__wrnexus/styles.css`. */
 export interface DevStyles {
@@ -99,6 +100,7 @@ export function createDevAssetServer(
       if (pathname.startsWith("/__wrnexus/island/")) {
         return serveIslandArtifact(pathname) ?? new Response("Not Found", { status: 404 });
       }
+      if (pathname === HMR_CLIENT_HREF) return jsResponse(HMR_CLIENT_JS);
       if (pathname === "/__wrnexus/islands.js") return jsResponse(getIslandRuntime(true));
       if (pathname === "/__wrnexus/reactive.js") return jsResponse(getReactiveRuntime(true));
       if (pathname === "/__wrnexus/controllers.js")