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/e2e/tests/clients.spec.ts

@@ -63,3 +63,52 @@ test("clicking a client shows their details", async ({ page }) => {
   // Email appears in both the list row and the detail panel once selected
   await expect(page.getByText("alice@example.com")).toHaveCount(2);
 });
+
+test("direct URL navigation to client detail fetches data and renders client name", async ({ page }) => {
+  // Mock individual client fetch for direct navigation
+  await page.route("/api/clients/client-1", (route) =>
+    route.fulfill({ json: MOCK_CLIENTS[0] })
+  );
+  // Mock pets for this client
+  await page.route("/api/pets**", (route) =>
+    route.fulfill({ json: [] })
+  );
+
+  await page.goto("/admin/clients/client-1");
+  // Client name must be visible without any clicking
+  await expect(page.getByText("Alice Johnson")).toBeVisible();
+  // Should show back to list link
+  await expect(page.getByText("← Back to list")).toBeVisible();
+});
+
+test("direct URL navigation shows loading then client", async ({ page }) => {
+  let resolvePets: (value: unknown) => void;
+  const petsPromise = new Promise((resolve) => { resolvePets = resolve; });
+
+  await page.route("/api/clients/client-1", (route) =>
+    route.fulfill({ json: MOCK_CLIENTS[0] })
+  );
+  await page.route("/api/pets**", async (route) => {
+    await petsPromise;
+    await route.fulfill({ json: [] });
+  });
+
+  const navigationPromise = page.goto("/admin/clients/client-1");
+  // Should show loading state briefly
+  await expect(page.getByText("Loading client…")).toBeVisible();
+  // Resolve pets and wait for navigation
+  resolvePets!();
+  await navigationPromise;
+  // After data loads, client name is shown
+  await expect(page.getByText("Alice Johnson")).toBeVisible();
+});
+
+test("direct URL navigation shows error state on failure", async ({ page }) => {
+  await page.route("/api/clients/nonexistent", (route) =>
+    route.fulfill({ status: 404, json: { error: "Client not found" } })
+  );
+
+  await page.goto("/admin/clients/nonexistent");
+  await expect(page.getByText(/client not found/i)).toBeVisible();
+  await expect(page.getByText("← Back to clients")).toBeVisible();
+});