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/tsconfig.json

@@ -0,0 +1,34 @@
+{
+  "compilerOptions": {
+    "target": "es2020", // https://github.com/microsoft/TypeScript/wiki/Node-Target-Mapping
+    "module": "commonjs",
+    "esModuleInterop": true, // solves the problem regarding the default importa vs importa *
+    "strict": true,
+    "sourceMap": true, // please do create source maps
+    "skipLibCheck": true, // don't verify typescript of 3rd party modules
+    "rootDir": "src", // root directory under which source files are located - it's subtree will be mirrored in "outDir"
+    "outDir": "build", // where the build files should be stored
+// "baseUrl" ----- DO NOT USE ... heres why:
+                // NOTE: if "baseUrl" is set then Intellisense while doing autocompletion (Ctrl+Space)
+                //       will use and insert absolute module path instead of relative one,
+                //       which will make the build fail
+                //      "baseUrl": "./", // set a base directory to resolve non-absolute module names - This must be specified if "paths" is used
+    "plugins": [
+      {
+        // The following is used for when building the project
+        // NOTE: build is done by `ttypescript`
+        //       which does not know how to interpret what is set in "paths"
+        //       > this problem is fixed by "typescript-transform-paths"
+        "transform": "typescript-transform-paths"
+      }
+    ]
+  },
+  "include": ["src/**/*"], // location of files which need to be compiled
+  // The following is used for debugging the server in VS Code
+  // NOTE: when debugging the module is started using `ts-node`,
+  //       which does not know how to interpret what is set in "paths"
+  //       > this is fixed by "tsconfig-paths/register"
+  "ts-node": {
+    "require": ["tsconfig-paths/register"]
+  },
+}