fix(client): give the portal row an icon, and assert every gated nav has one

The §7.7 smoke, running the pair together: registering the player row without an
`icon` blanked the whole portal with React error #130, because core's
PlayerPortalLayout rendered `<n.icon />` unguarded. Core is guarded now
(website), and this is the other half — the row had an icon before it moved and
should have kept one.

A second glyph rather than reusing IconShard: these two rows sit in different
navs and each matched its neighbours before the extraction. The admin sidebar's
UO rows were gems; the portal's Characters row was a person beside Appeals'
shield and Account's gear. Matching the nav a row lands in is the whole reason
`icon` is in the contract.

`registration.test.js` now asserts it for admin AND player rows, which is the
cheap place to catch the next one. The public header is text buttons and is
deliberately excluded.

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

client/src/entry.jsx

@@ -18,7 +18,7 @@
 // size and it is the one thing this seam cannot have.
 
 import { registry, coreApiVersion } from './core.js'
-import { IconShard } from './icons.jsx'
+import { IconShard, IconUser } from './icons.jsx'
 import { useShardFlags } from './lib/useShardFeatures.js'
 
 // Public pages — the twelve that used to live at /site/*.
@@ -159,7 +159,7 @@ registry.registerNav(ID, {
   area: 'player',
   // Order 0: Characters is the portal's first row today, and with the module
   // installed it is also what core's `/player` index resolves to.
-  items: [{ label: 'Characters', to: '/player/uo/characters', order: 0 }],
+  items: [{ label: 'Characters', to: '/player/uo/characters', icon: IconUser, order: 0 }],
 })
 
 // ── Feature provider ───────────────────────────────────────────────────────