[Teams] Public channel become in fact private if added to Private Team

Description:

Most common case of using Teams feature, IMHO, is to create a Private Team and add some channels to that Team, including Public Channels of cause. But in that case that Public Channels start behave like Private groups, which is wrong.

Steps to reproduce:

1. Create Private Team
2. Add Public Channel to that Private Team
3. Public Channel not shown in search result, so become a Private Group
4. In Admin UI that Public Channel remain to be Public Channel

Expected behavior:

Public Channels should remain public if they added to Private Team

Actual behavior:

As on screenshot DevOps Corp is a Private Team and DevOps is Public Channel which was added to DevOps Corp

But that DevOps is Public channel not available in Directory Search

Server Setup Information:

• Version of Rocket.Chat Server: 3.15.0
• Operating System: CentOS7
• Deployment Method: docker
• Number of Running Instances: 25
• DB Replicaset Oplog: Enabled
• NodeJS Version: 12.22.1
• MongoDB Version: 4.2.14 WiredTiger

Client Setup Information

• Desktop App or Browser Version: 3.2.2
• Operating System: Windows 10

Additional context

Relevant logs:

Reproduce the issue with a Private Team, a Public Channel, and Directory Search, then compare the channel's visibility in the Admin UI. No source files or tests are named; trace the Teams and Directory Search entry points to identify where team privacy affects public-channel discoverability. Done means the channel remains searchable while retaining its public status.