feat: add webhook support for real-time Autotask updates

Implements comprehensive webhook infrastructure to receive and process
real-time entity updates from Autotask, reducing API calls and improving
data freshness.

Features:
- Webhook receiver endpoint: POST /api/webhooks/autotask
- Automatic entity mapping and upsert to PostgreSQL
- Event logging and tracking in webhook_logs table
- Duplicate event prevention via unique event_id
- Failed event tracking with error messages
- Statistics and monitoring APIs
- Support for 8 entity types: Companies, Tickets, Tasks, Projects,
  Time Entries, Contacts, Contracts, Configuration Items

Architecture:
- WebhookService: Core processing logic
- Database tables: webhook_logs, webhook_configs
- API endpoints: /autotask (receiver), /logs, /stats
- Automatic data mapping using existing entity-mapper

Benefits:
- Near real-time updates (<1 minute vs 24 hours)
- Reduced API usage (webhooks vs polling)
- Complements daily incremental sync for redundancy
- Automatic recovery from webhook failures

Files Added:
- lib/types/webhook.ts - TypeScript types and interfaces
- lib/services/webhook-service.ts - Webhook processing service
- app/api/webhooks/autotask/route.ts - Webhook receiver
- app/api/webhooks/logs/route.ts - Logs API
- app/api/webhooks/stats/route.ts - Statistics API
- migrations/004_webhook_support.sql - Database schema
- docs/WEBHOOK_SETUP.md - Complete setup guide (47 sections)
- docs/WEBHOOKS_README.md - Quick start guide

Next Steps:
1. Run database migration
2. Configure webhooks in Autotask
3. Test endpoint and monitor logs

See docs/WEBHOOK_SETUP.md for detailed setup instructions.

lib/types/webhook.ts

@@ -0,0 +1,110 @@
+/**
+ * Autotask Webhook Types
+ * Based on: https://autotask.net/help/DeveloperHelp/Content/APIs/Webhooks/WEBHOOKS.htm
+ */
+
+/**
+ * Webhook event types from Autotask
+ */
+export enum WebhookEventType {
+  CREATE = 'create',
+  UPDATE = 'update',
+  DELETE = 'delete',
+}
+
+/**
+ * Supported entity types for webhooks
+ */
+export enum WebhookEntityType {
+  COMPANIES = 'Companies',
+  TICKETS = 'Tickets',
+  TASKS = 'Tasks',
+  PROJECTS = 'Projects',
+  TIME_ENTRIES = 'TimeEntries',
+  CONTACTS = 'Contacts',
+  CONTRACTS = 'Contracts',
+  CONFIGURATION_ITEMS = 'ConfigurationItems',
+}
+
+/**
+ * Autotask webhook payload structure
+ */
+export interface AutotaskWebhookPayload {
+  /**
+   * Unique identifier for the webhook event
+   */
+  eventId: string;
+
+  /**
+   * Type of event (create, update, delete)
+   */
+  eventType: WebhookEventType;
+
+  /**
+   * Entity type that triggered the webhook
+   */
+  entityType: WebhookEntityType;
+
+  /**
+   * ID of the entity that changed
+   */
+  entityId: number;
+
+  /**
+   * Timestamp when the event occurred
+   */
+  eventTimestamp: string;
+
+  /**
+   * Optional: Full entity data (if configured in webhook)
+   */
+  entity?: Record<string, any>;
+
+  /**
+   * Optional: Previous values for update events
+   */
+  previousValues?: Record<string, any>;
+}
+
+/**
+ * Webhook processing result
+ */
+export interface WebhookProcessingResult {
+  success: boolean;
+  eventId: string;
+  entityType: WebhookEntityType;
+  entityId: number;
+  action: 'created' | 'updated' | 'deleted' | 'skipped';
+  error?: string;
+  processingTime: number;
+}
+
+/**
+ * Webhook log entry for tracking
+ */
+export interface WebhookLog {
+  id?: number;
+  event_id: string;
+  entity_type: string;
+  entity_id: number;
+  event_type: WebhookEventType;
+  status: 'pending' | 'processed' | 'failed';
+  error_message?: string;
+  received_at: Date;
+  processed_at?: Date;
+  processing_time_ms?: number;
+  payload: Record<string, any>;
+}
+
+/**
+ * Webhook configuration
+ */
+export interface WebhookConfig {
+  id?: number;
+  entity_type: WebhookEntityType;
+  event_types: WebhookEventType[];
+  is_active: boolean;
+  autotask_webhook_id?: string;
+  created_at?: Date;
+  updated_at?: Date;
+}