feature: a minimal implementation of the appointment feature done.

backend/prisma/schema.prisma

@@ -60,6 +60,7 @@ model Organization {
   sharedWithOthers OrganizationLink[] @relation("OrganizationA")
   sentOrganizationInvitations OrganizationInvitation[] @relation("OrganizationInvitationInviter")
   patients         Patient[]
+  appointments     Appointment[]
 
   createdAt DateTime @default(now())
   updatedAt DateTime @updatedAt
@@ -82,6 +83,7 @@ model Patient {
 
   organization Organization             @relation(fields: [organizationId], references: [id])
   treatments   PatientTreatmentHistory[]
+  appointments Appointment[]
 
   @@index([organizationId, createdAt])
   @@index([organizationId, lastName, firstName])
@@ -106,6 +108,26 @@ model PatientTreatmentHistory {
   @@map("patient_treatment_histories")
 }
 
+model Appointment {
+  id             String   @id @default(uuid())
+  organizationId String
+  patientId      String
+  providerUserId String
+  startAt        DateTime
+  endAt          DateTime
+  purpose        String
+
+  organization Organization @relation(fields: [organizationId], references: [id], onDelete: Cascade)
+  patient      Patient      @relation(fields: [patientId], references: [id], onDelete: Cascade)
+
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+
+  @@index([organizationId, providerUserId, startAt])
+  @@index([organizationId, startAt])
+  @@map("appointments")
+}
+
 model Plan {
   id       String @id @default(uuid())
   name     String @unique // "Solo", "Small", "Medium", "Large", "Enterprise"