feat: implement MailGun webhook service for logging email events

Implemented a production-ready TypeScript/Express.js service to receive
and log MailGun webhook events (delivered, failed, opened, clicked, etc.).

Key features:
- Webhook endpoint (POST /webhook) with comprehensive event logging
- Full TypeScript type definitions for all MailGun event types
- Prometheus metrics integration for monitoring
- Health check endpoint (GET /ping)
- Comprehensive Jest test suite with 87.76% coverage
- Docker containerization with build scripts

Removed template/example code:
- All SQL/MSSQL dependencies and related code
- Example auth router and middleware
- PRTG metrics support (simplified to Prometheus only)
- Unused middleware (CORS, IP whitelist, request parsing/validation)
- Template documentation (kept only MailGun webhook API spec)

The service is clean, minimal, and focused solely on receiving and
logging MailGun webhook events to the console.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

mailgun-webhook/tests/helpers/mockHttpContext.ts

@@ -0,0 +1,59 @@
+/**
+ * @fileoverview
+ * This file is a part of an "auth" example router, which was taken from an existing integration.
+ * It is to be used only as a reference for how an API router for a web service should be structured.
+ * In a real-live implementation all files related to `/auth` route example should be removed
+ * by new set of files implementing the new API.
+ */
+import { Request, Response, NextFunction } from 'express';
+import { AppLocals } from "../../src/types/AppLocals";
+
+interface IMockHttpParams {
+  sessionID?: number
+  sessionGUID?: string
+  table_id?: string
+  clientIp?: string
+  free_play: 0 | 1
+}
+
+interface IMockHttpContext {
+  clientIpAddress?:string
+  reqPath?:string
+  headersSent?:boolean
+  writableEnded?:boolean
+  method?:string
+  params?: IMockHttpParams
+}
+
+export const defaultMockParams:IMockHttpParams = {
+  sessionID: 123,
+  sessionGUID: '016e6812-b915-4e5e-94fe-193582239b96',
+  table_id: 'mock-table-id',
+  clientIp: '192.168.1.10',
+  free_play: 0
+}
+
+export const mockHttpContext = ({reqPath="/", headersSent=false, writableEnded=false, method="GET", params=defaultMockParams}:IMockHttpContext|undefined = {}) => {
+    const req = {
+      path:reqPath,
+      method,
+      url:`https://localhost${reqPath}`,
+      params,
+    } as unknown as Request;
+  
+    const res = {
+      end: jest.fn(),
+      status: jest.fn(),
+      setHeader: jest.fn(),
+      params,
+      locals: {
+        stopPrometheusTimer: jest.fn(),
+      } as unknown as AppLocals,
+      headersSent,
+      writableEnded,
+    } as unknown as Response;
+
+    const next:NextFunction = jest.fn();
+  
+    return({req,res,next})
+  }