fix: address review — pin .xml alias in MIME_BY_EXT, hoist fallback above condition

- Pin '.xml': 'text/xml' in MIME_BY_EXT overrides to prevent
  application/xml from overwriting text/xml in the reversed map
- Move mediaType ??= fallback above the if-guard in send-api.ts
  for clarity (avoids side-effect assignment inside condition)

extensions/whatsapp/src/inbound/send-api.ts

@@ -34,7 +34,8 @@ export function createWebSendApi(params: {
     ): Promise<{ messageId: string }> => {
       const jid = toWhatsappJid(to);
       let payload: AnyMessageContent;
-      if (mediaBuffer && (mediaType ??= "application/octet-stream")) {
+      mediaType ??= "application/octet-stream";
+      if (mediaBuffer && mediaType) {
         if (mediaType.startsWith("image/")) {
           payload = {
             image: mediaBuffer,

src/media/mime.ts

@@ -48,6 +48,7 @@ const MIME_BY_EXT: Record<string, string> = {
   ".jpeg": "image/jpeg",
   ".js": "text/javascript",
   ".htm": "text/html",
+  ".xml": "text/xml", // pin text/xml as canonical (application/xml also maps to .xml in EXT_BY_MIME)
 };
 
 const AUDIO_FILE_EXTENSIONS = new Set([