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/shared/schemas/results/UserAggregateResult.schema.ts

@@ -23,7 +23,8 @@ export const UserAggregateResultSchema = z.object({  _count: z.object({
     officeHours: z.number(),
     officeContact: z.number(),
     procedureTimeslot: z.number(),
-    insuranceContacts: z.number()
+    insuranceContacts: z.number(),
+    patientConversations: z.number()
   }).optional(),
   _sum: z.object({
     id: z.number().nullable()