fix(html): move router constants to ui/constants.mjs; keep node: imports out of browser bundle

constants.mjs imports node:path and node:url, which break when bundled for
the browser. The ROUTER_* constants added in da720ce pulled those Node.js
builtins into the client bundle, silently preventing startRouter from loading
and causing every client-side navigation to fall back to a full page reload.

Move the constants to packages/react/src/html/ui/constants.mjs (browser-only
code) and remove their exports from the Node.js-side constants.mjs.

Assisted-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ovflowd

packages/react/src/html/constants.mjs

@@ -92,12 +92,3 @@ export const FONTS = [
   'open-sans-latin-wght-italic.woff2',
   'ibm-plex-mono-latin-400-normal.woff2',
 ];
-
-// How long a hovered link waits before its page is prefetched.
-export const ROUTER_HOVER_DELAY = 80;
-
-// How long a fetched page is reused for, whether prefetched or visited.
-export const ROUTER_PAGE_LIFETIME = 5 * 60 * 1000;
-
-// How many fetched pages are kept at once.
-export const ROUTER_MAX_PAGES = 10;

packages/react/src/html/ui/constants.mjs

@@ -0,0 +1,8 @@
+// How long a hovered link waits before its page is prefetched.
+export const ROUTER_HOVER_DELAY = 80;
+
+// How long a fetched page is reused for, whether prefetched or visited.
+export const ROUTER_PAGE_LIFETIME = 5 * 60 * 1000;
+
+// How many fetched pages are kept at once.
+export const ROUTER_MAX_PAGES = 10;

packages/react/src/html/ui/router.mjs

@@ -22,7 +22,7 @@ import {
   ROUTER_HOVER_DELAY,
   ROUTER_MAX_PAGES,
   ROUTER_PAGE_LIFETIME,
-} from '../constants.mjs';
+} from './constants.mjs';
 import { fetchPage, parsePage, showPage, transition } from './page.mjs';
 
 /**