feat: update Mattermost proxy configuration and documentation for improved clarity and default behavior

scripts/mattermost-proxy/mattermost_mirror.py

@@ -147,7 +147,11 @@ class MattermostMirror:
         host = host.lower()
         if self.host_allow:
             return host == self.host_allow or host.endswith(f".{self.host_allow}")
-        return "mattermost" in host
+        # The launched Mattermost Desktop app is already scoped to this proxy.
+        # Some company hosts do not include "mattermost" in the hostname
+        # (for example, mm.example.com), so default to allowing the proxied
+        # app's /api/v4 traffic when no explicit host allowlist is configured.
+        return True
 
     def _is_allowed_channel(self, channel_id: str | None) -> bool:
         if not self.channel_allow: