fix(GRO-743): add dedicated client detail route with unconditional data fetch (#316)

Direct navigation to /admin/clients/{id} now:
- Fetches GET /api/clients/{id} on mount (unconditional)
- Fetches GET /api/pets?clientId= on mount
- Shows loading state while fetching
- Shows error state on failure (401/404/5xx)
- Preserves existing link-based navigation from ClientsPage

Added ClientDetailPage.tsx as a standalone route component.
Added 3 E2E tests covering direct nav, loading state, and error state.

Co-authored-by: Test User <test@example.com>
Co-authored-by: Paperclip <noreply@paperclip.ing>

apps/web/src/App.tsx

@@ -2,6 +2,7 @@ import { Routes, Route, Link, useLocation, Navigate, useNavigate } from "react-r
 import { useEffect, useState } from "react";
 import { AppointmentsPage } from "./pages/Appointments.js";
 import { ClientsPage } from "./pages/Clients.js";
+import { ClientDetailPage } from "./pages/ClientDetailPage.js";
 import { ServicesPage } from "./pages/Services.js";
 import { StaffPage } from "./pages/Staff.js";
 import { InvoicesPage } from "./pages/Invoices.js";
@@ -296,6 +297,7 @@ function AdminLayout() {
         <Routes>
           <Route path="/" element={<AppointmentsPage />} />
           <Route path="/clients" element={<ClientsPage />} />
+          <Route path="/clients/:clientId" element={<ClientDetailPage />} />
           <Route path="/services" element={<ServicesPage />} />
           <Route path="/staff" element={<StaffPage />} />
           <Route path="/invoices" element={<InvoicesPage />} />