Replace hardcoded time slots with dynamic API availability

Both BookingFlow and RescheduleFlow in Appointments.tsx now fetch
from /api/book/availability when a date is selected, matching the
public booking wizard behavior. Loading and error states shown.

- Removed hardcoded availableTimes arrays from both flows
- Added useEffect that fetches availability on date change
- Shows "Checking availability…" while loading
- Shows error message on fetch failure
- Shows "No available slots" when API returns empty

Added tests for RescheduleFlow dynamic slot fetching covering:
loading, fetched slots, error, empty, API params, and re-fetch on
date change.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/__tests__/Appointments.test.tsx

@@ -1,5 +1,5 @@
 import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
-import { render, screen, fireEvent, waitFor } from "@testing-library/react";
+import { render, screen, fireEvent, waitFor, act } from "@testing-library/react";
 import { parseTimeTo24Hour, isUpcoming, CustomerNotesSection, ConfirmationSection } from "../portal/sections/Appointments.tsx";
 
 const UPCOMING_APPT = {
@@ -379,4 +379,142 @@ describe("ConfirmationSection", () => {
       expect(screen.getByText(/Confirmed!/i)).toBeInTheDocument();
     });
   });
+});
+
+describe("RescheduleFlow dynamic time slots", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    global.fetch = vi.fn();
+  });
+
+  const RESCHEDULE_APPT = {
+    id: "appt-r1",
+    petId: "pet-1",
+    petName: "Buddy",
+    groomerId: "groomer-1",
+    groomerName: "Sarah",
+    services: ["Bath & Brush"],
+    serviceId: "service-1",
+    addOns: [],
+    date: "2027-01-01",
+    time: "10:00 AM",
+    duration: 60,
+    price: 50,
+    status: "confirmed" as const,
+    notes: "",
+    customerNotes: "",
+    confirmationStatus: "confirmed" as const,
+  };
+
+  it("shows loading state while fetching availability", async () => {
+    vi.mocked(global.fetch).mockReturnValue(new Promise(() => {})); // Never resolves
+
+    const { RescheduleFlow } = await import("../portal/sections/Appointments.tsx");
+    render(<RescheduleFlow appointment={RESCHEDULE_APPT} onClose={() => {}} sessionId="test-session-id" />);
+
+    const dateInput = screen.getByLabelText(/date/i) || screen.getByRole("textbox", { name: /date/i });
+    fireEvent.change(dateInput, { target: { value: "2027-01-15" } });
+
+    await waitFor(() => {
+      expect(screen.getByText(/Checking availability/i)).toBeInTheDocument();
+    });
+  });
+
+  it("displays fetched time slots from API", async () => {
+    vi.mocked(global.fetch).mockResolvedValue({
+      ok: true,
+      json: async () => ["9:00 AM", "10:00 AM", "2:00 PM"],
+    } as Response);
+
+    const { RescheduleFlow } = await import("../portal/sections/Appointments.tsx");
+    render(<RescheduleFlow appointment={RESCHEDULE_APPT} onClose={() => {}} sessionId="test-session-id" />);
+
+    const dateInput = screen.getByLabelText(/date/i) || screen.getByRole("textbox", { name: /date/i });
+    fireEvent.change(dateInput, { target: { value: "2027-01-15" } });
+
+    await waitFor(() => {
+      expect(screen.getByText("9:00 AM")).toBeInTheDocument();
+      expect(screen.getByText("10:00 AM")).toBeInTheDocument();
+      expect(screen.getByText("2:00 PM")).toBeInTheDocument();
+    });
+  });
+
+  it("shows error state when availability fetch fails", async () => {
+    vi.mocked(global.fetch).mockRejectedValue(new Error("Network error"));
+
+    const { RescheduleFlow } = await import("../portal/sections/Appointments.tsx");
+    render(<RescheduleFlow appointment={RESCHEDULE_APPT} onClose={() => {}} sessionId="test-session-id" />);
+
+    const dateInput = screen.getByLabelText(/date/i) || screen.getByRole("textbox", { name: /date/i });
+    fireEvent.change(dateInput, { target: { value: "2027-01-15" } });
+
+    await waitFor(() => {
+      expect(screen.getByText(/Failed to load time slots/i)).toBeInTheDocument();
+    });
+  });
+
+  it("shows no slots message when API returns empty array", async () => {
+    vi.mocked(global.fetch).mockResolvedValue({
+      ok: true,
+      json: async () => [] as string[],
+    } as Response);
+
+    const { RescheduleFlow } = await import("../portal/sections/Appointments.tsx");
+    render(<RescheduleFlow appointment={RESCHEDULE_APPT} onClose={() => {}} sessionId="test-session-id" />);
+
+    const dateInput = screen.getByLabelText(/date/i) || screen.getByRole("textbox", { name: /date/i });
+    fireEvent.change(dateInput, { target: { value: "2027-01-15" } });
+
+    await waitFor(() => {
+      expect(screen.getByText(/No available slots on this date/i)).toBeInTheDocument();
+    });
+  });
+
+  it("calls /api/book/availability with the selected date", async () => {
+    vi.mocked(global.fetch).mockResolvedValue({
+      ok: true,
+      json: async () => ["9:00 AM"] as string[],
+    } as Response);
+
+    const { RescheduleFlow } = await import("../portal/sections/Appointments.tsx");
+    render(<RescheduleFlow appointment={RESCHEDULE_APPT} onClose={() => {}} sessionId="test-session-id" />);
+
+    const dateInput = screen.getByLabelText(/date/i) || screen.getByRole("textbox", { name: /date/i });
+    fireEvent.change(dateInput, { target: { value: "2027-02-20" } });
+
+    await waitFor(() => {
+      expect(global.fetch).toHaveBeenCalledWith(
+        "/api/book/availability?date=2027-02-20",
+        expect.objectContaining({
+          headers: expect.objectContaining({ "X-Impersonation-Session-Id": "test-session-id" }),
+        })
+      );
+    });
+  });
+
+  it("re-fetches slots when date changes", async () => {
+    vi.mocked(global.fetch)
+      .mockResolvedValueOnce({
+        ok: true,
+        json: async () => ["9:00 AM"] as string[],
+      } as Response)
+      .mockResolvedValueOnce({
+        ok: true,
+        json: async () => ["11:00 AM", "1:00 PM"] as string[],
+      } as Response);
+
+    const { RescheduleFlow } = await import("../portal/sections/Appointments.tsx");
+    render(<RescheduleFlow appointment={RESCHEDULE_APPT} onClose={() => {}} sessionId="test-session-id" />);
+
+    const dateInput = screen.getByLabelText(/date/i) || screen.getByRole("textbox", { name: /date/i });
+
+    fireEvent.change(dateInput, { target: { value: "2027-01-10" } });
+    await waitFor(() => expect(screen.getByText("9:00 AM")).toBeInTheDocument());
+
+    fireEvent.change(dateInput, { target: { value: "2027-01-15" } });
+    await waitFor(() => {
+      expect(screen.getByText("11:00 AM")).toBeInTheDocument();
+      expect(screen.getByText("1:00 PM")).toBeInTheDocument();
+    });
+  });
 });