improvement: appointment dialog UX improved.

frontend/messages/en.json

@@ -546,6 +546,9 @@
     "endLabel": "End",
     "purposeLabel": "Purpose",
     "errorSelectPatient": "Select a patient first.",
+    "patientSearchPlaceholder": "Search patients by name, phone, or email",
+    "patientSearchEmpty": "No patients match this search.",
+    "patientLockedHint": "Patient cannot be changed because a treatment is linked to this appointment.",
     "errorEndAfterStart": "End time must be after start time.",
     "errorPastSchedule": "Cannot schedule in the past.",
     "errorPastViewOnly": "Past appointments are view-only.",
@@ -901,6 +904,7 @@
     "NOT_FOUND": "The requested item was not found.",
     "CONFLICT": "This action conflicts with existing data.",
     "CONFLICT_FUTURE_APPOINTMENTS": "You cannot stop participating in treatments while you have future appointments. Reassign or cancel them first.",
+    "APPOINTMENT_PATIENT_LOCKED": "Cannot change the patient while a treatment is linked to this appointment.",
     "BAD_REQUEST": "The request could not be processed.",
     "INTERNAL_ERROR": "Something went wrong on our end. Please try again later."
   }