fix(portal): disable non-functional Reschedule buttons (GRO-166)

Commit b3a3f80 removed disabled/stub attributes from Reschedule
buttons but never implemented the onClick handlers. Buttons were
enabled but inert — clicking did nothing, perceived as "blank page."

Restore disabled state with "Rescheduling — coming soon" tooltip
to both Dashboard and Appointments Reschedule buttons.

Full reschedule flow requires a /api/portal/appointments/:id/reschedule
endpoint — tracked separately.

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

apps/web/src/portal/sections/Appointments.tsx

@@ -176,7 +176,12 @@ function AppointmentCard({
           )}
           {appt.status !== "completed" && appt.status !== "cancelled" && !readOnly && (
             <div className="flex gap-2 mt-3">
-              <button className="text-xs px-3 py-1.5 border border-stone-200 rounded-lg text-stone-600 hover:bg-stone-50">
+              <button
+                type="button"
+                disabled
+                title="Rescheduling — coming soon"
+                className="text-xs px-3 py-1.5 border border-stone-200 rounded-lg text-stone-400 cursor-not-allowed"
+              >
                 Reschedule
               </button>
               <CancelAppointmentButton appointment={appt} sessionId={sessionId} />

apps/web/src/portal/sections/Dashboard.tsx

@@ -77,7 +77,12 @@ export function Dashboard({ onNavigate, readOnly }: Props) {
           </div>
           {!readOnly && (
             <div className="flex gap-2 mt-4">
-              <button className="text-sm px-3 py-1.5 border border-stone-200 rounded-lg text-stone-600 hover:bg-stone-50">
+              <button
+                type="button"
+                disabled
+                title="Rescheduling — coming soon"
+                className="text-sm px-3 py-1.5 border border-stone-200 rounded-lg text-stone-400 cursor-not-allowed"
+              >
                 Reschedule
               </button>
               <button className="text-sm px-3 py-1.5 border border-stone-200 rounded-lg text-stone-600 hover:bg-stone-50">