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/objects/PatientConversationArgs.schema.ts

@@ -0,0 +1,11 @@
+import * as z from 'zod';
+import type { Prisma } from '../../../generated/prisma';
+import { PatientConversationSelectObjectSchema as PatientConversationSelectObjectSchema } from './PatientConversationSelect.schema';
+import { PatientConversationIncludeObjectSchema as PatientConversationIncludeObjectSchema } from './PatientConversationInclude.schema'
+
+const makeSchema = () => z.object({
+  select: z.lazy(() => PatientConversationSelectObjectSchema).optional(),
+  include: z.lazy(() => PatientConversationIncludeObjectSchema).optional()
+}).strict();
+export const PatientConversationArgsObjectSchema = makeSchema();
+export const PatientConversationArgsObjectZodSchema = makeSchema();