feat(admin): view a user's shard footprint at /admin/users/:id

Add a "View" action beside Edit in the users table that opens a dedicated,
read-only page showing everything the uo-link shard knows about a user,
scoped to their linked game accounts: character rosters, currently-online
characters, houses (IDOC-first), and recent vendor sales.

Backend (admin-only, under the existing /users adminOnly gate):
- GET /admin/users/:id — single sanitized user (page is deep-linkable)
- GET /admin/users/:id/shard/{accounts,sales,houses,online}
- shardState: listHousesByAccounts / listOnlineByAccounts (+ model shapers)
- Extract salesForAccounts into utils/shardSales; reuse in player getSales
- Live rosters reuse the existing admin-bypass /admin/shard/* endpoints,
  so no new routes for roster/vendors/char

Frontend:
- UserDetail page reusing CharacterStats / GameAccounts / VendorSales
- GameAccounts gains a readOnly prop (drops link form + self-voice copy)
- api.admin.getUser + api.admin.userShard(id) scope; route + layout title

Tests: adminUserShard.test.js (404, account scoping, empty accounts,
salesForAccounts cap/filter). Full server suite 164 pass; client builds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0114TpmrNW4wNXsHq5CR72jQ

client/src/App.jsx

@@ -40,6 +40,7 @@ import AdminCharacters from './routes/admin/views/AdminCharacters.jsx'
 import AdminCharacter from './routes/admin/views/AdminCharacter.jsx'
 import AuthProvidersAdmin from './routes/admin/views/AuthProvidersAdmin.jsx'
 import UsersAdmin from './routes/admin/views/UsersAdmin.jsx'
+import UserDetail from './routes/admin/views/UserDetail.jsx'
 import AccountAdmin from './routes/admin/views/AccountAdmin.jsx'
 import Moderation from './routes/admin/views/Moderation.jsx'
 import ModerationUser from './routes/admin/views/ModerationUser.jsx'
@@ -124,6 +125,7 @@ export default function App() {
             <Route path="characters/:serial" element={<AdminCharacter />} />
             <Route path="auth-providers" element={<AuthProvidersAdmin />} />
             <Route path="users" element={<UsersAdmin />} />
+            <Route path="users/:id" element={<UserDetail />} />
             <Route path="account" element={<AccountAdmin />} />
             <Route path="*" element={<Navigate to="/admin" replace />} />
           </Route>