Add public Shard page + player Game Accounts UI (phase 4)

Frontend for the uo-link integration, matching the existing site styling.

- api/client.js: api.shard.* (status/feed/economy/idoc/char), the
  shardStreamUrl SSE endpoint, and api.player.shard.* (link/accounts/roster/
  vendors).
- lib/useShardFeed.js: EventSource hook over /public/shard/stream with a
  rolling buffer and a connected flag (browser never touches the sidecar WS).
- routes/public/Shard.jsx: connection banner, stat tiles (online / gold supply
  / link), a gold-supply sparkline, "recent vendor sales" and "IDOC houses"
  lists, and a live event ticker — built from the shared panel/grid/format
  vocabulary. Registered at /site/shard under the maintenance gate and linked
  from the site header.
- routes/player/PlayerAccount.jsx: a "Game accounts" section — enter a [link
  code to link an account, then expand it to see characters and player vendors
  on demand (503 shows a retry banner).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011qPmpmVH1xGCiZoz9m9vW3

client/src/App.jsx

@@ -16,6 +16,7 @@ import Newsletter from './routes/public/Newsletter.jsx'
 import NewsletterIssue from './routes/public/NewsletterIssue.jsx'
 import About from './routes/public/About.jsx'
 import Status from './routes/public/Status.jsx'
+import Shard from './routes/public/Shard.jsx'
 import Wiki from './routes/wiki/Wiki.jsx'
 import WikiArticle from './routes/wiki/WikiArticle.jsx'
 import CmsPage from './routes/public/CmsPage.jsx'
@@ -66,6 +67,7 @@ export default function App() {
             <Route path="/site/newsletter/:id" element={<NewsletterIssue />} />
             <Route path="/site/about" element={<About />} />
             <Route path="/site/status" element={<Status />} />
+            <Route path="/site/shard" element={<Shard />} />
             <Route path="/wiki" element={<Wiki />} />
             <Route path="/wiki/:slug" element={<WikiArticle />} />
             {/* CMS pages: top-level /:slug, matched only after the named routes