fix: append IST offset (+05:30) to bare datetime in appointment booking

Widget and WhatsApp flows send scheduledAt without timezone offset,
causing platform to interpret as UTC (10:00 shows as 3:30 PM IST).
Server now appends +05:30 if no timezone indicator present. Also fixed
in WhatsApp slot ID generation and widget source.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/messaging/flow/tool-registry.ts

@@ -142,7 +142,7 @@ export class ToolRegistry {
             const sections: ListSection[] = [{
                 title: targetDate,
                 rows: timeSlots.map(s => ({
-                    id: `slot:${doctorId}:${targetDate}T${s.time}:00`,
+                    id: `slot:${doctorId}:${targetDate}T${s.time}:00+05:30`,
                     title: s.time,
                     description: s.clinic || undefined,
                 })),
@@ -202,7 +202,7 @@ export class ToolRegistry {
             // Book — include patientId so appointment is linked to patient record
             const result = await this.platform.query<any>(
                 `mutation($data: AppointmentCreateInput!) { createAppointment(data: $data) { id } }`,
-                { data: { name: `WhatsApp Booking — ${patientName} (${department})`, scheduledAt, status: 'SCHEDULED', doctorName, department, reasonForVisit: reason ?? 'General Consultation', ...(patientId ? { patientId } : {}) } },
+                { data: { name: `WhatsApp Booking — ${patientName} (${department})`, scheduledAt: scheduledAt.includes('+') || scheduledAt.includes('Z') ? scheduledAt : `${scheduledAt}+05:30`, status: 'SCHEDULED', doctorName, department, reasonForVisit: reason ?? 'General Consultation', ...(patientId ? { patientId } : {}) } },
             );
             const id = result?.createAppointment?.id;
             if (id) {

src/widget/widget.service.ts

@@ -235,7 +235,10 @@ export class WidgetService {
             `mutation($data: AppointmentCreateInput!) { createAppointment(data: $data) { id } }`,
             { data: {
                 name: `${req.patientName.trim() || 'Patient'} — ${new Date(req.scheduledAt).toISOString().slice(0, 10)}`,
-                scheduledAt: req.scheduledAt,
+                // Ensure IST offset — widget may send bare datetime without timezone
+                scheduledAt: req.scheduledAt.includes('+') || req.scheduledAt.includes('Z')
+                    ? req.scheduledAt
+                    : `${req.scheduledAt}+05:30`,
                 durationMin: 30,
                 appointmentType: 'CONSULTATION',
                 status: 'SCHEDULED',