Add MSG to EML email conversion support (#367)

- Add new msgconvert converter using libemail-outlook-message-perl
- Support conversion from Outlook MSG files to standard EML format
- Add msgconvert to Docker dependencies and version checking
- Register msgconvert converter in main converter registry

Implements feature request #367 for email format conversion

src/converters/msgconvert.ts

@@ -0,0 +1,47 @@
+import { execFile } from "node:child_process";
+
+export const properties = {
+  from: {
+    email: ["msg"],
+  },
+  to: {
+    email: ["eml"],
+  },
+};
+
+export function convert(
+  filePath: string,
+  fileType: string,
+  convertTo: string,
+  targetPath: string,
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
+  options?: unknown,
+): Promise<string> {
+  return new Promise((resolve, reject) => {
+    if (fileType === "msg" && convertTo === "eml") {
+      // Convert MSG to EML using msgconvert
+      // msgconvert will output to the same directory as the input file with .eml extension
+      // We need to use --outfile to specify the target path
+      const args = ["--outfile", targetPath, filePath];
+      
+      execFile("msgconvert", args, (error, stdout, stderr) => {
+        if (error) {
+          reject(`error: ${error}`);
+          return;
+        }
+
+        if (stdout) {
+          console.log(`stdout: ${stdout}`);
+        }
+
+        if (stderr) {
+          console.error(`stderr: ${stderr}`);
+        }
+
+        resolve("Done");
+      });
+    } else {
+      reject(`Unsupported conversion from ${fileType} to ${convertTo}. Only MSG to EML conversion is currently supported.`);
+    }
+  });
+}