feat: persist AI conversation state in DB and fix LangGraph flow bugs

- Replace in-memory Maps in aiHandoffStore with DB-backed async functions
  using new patient_conversation table (stage + aiHandoff per patient)
- Add afterHoursEnabled to ai_settings table (persists across restarts)
- Fix runtime crash in reschedule-graph: mon/tue/wed variables were out
  of scope in the next-week fallback branch (ReferenceError)
- Wire rescheduleGreeting and generalFallback chat templates through to
  LangGraph nodes so user-configured messages take effect
- Add otherNode to reminder-graph to handle unclassified patient replies
  (e.g. "I want another appointment") and route to booking flow
- Fetch chatTemplates once per webhook request instead of per stage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/db/generated/prisma/index-browser.js

@@ -421,7 +421,8 @@ exports.Prisma.TwilioSettingsScalarFieldEnum = {
 exports.Prisma.AiSettingsScalarFieldEnum = {
   id: 'id',
   userId: 'userId',
-  apiKey: 'apiKey'
+  apiKey: 'apiKey',
+  afterHoursEnabled: 'afterHoursEnabled'
 };
 
 exports.Prisma.OfficeHoursScalarFieldEnum = {
@@ -455,6 +456,15 @@ exports.Prisma.ProcedureTimeslotScalarFieldEnum = {
   data: 'data'
 };
 
+exports.Prisma.PatientConversationScalarFieldEnum = {
+  id: 'id',
+  patientId: 'patientId',
+  userId: 'userId',
+  stage: 'stage',
+  aiHandoff: 'aiHandoff',
+  updatedAt: 'updatedAt'
+};
+
 exports.Prisma.SortOrder = {
   asc: 'asc',
   desc: 'desc'
@@ -602,7 +612,8 @@ exports.Prisma.ModelName = {
   OfficeHours: 'OfficeHours',
   OfficeContact: 'OfficeContact',
   InsuranceContact: 'InsuranceContact',
-  ProcedureTimeslot: 'ProcedureTimeslot'
+  ProcedureTimeslot: 'ProcedureTimeslot',
+  PatientConversation: 'PatientConversation'
 };
 
 /**