[Browser MFA] Fix formatting in moderated sessions

[danielashare]

This PR fixes formatting when printing MFA messages to the terminal.

During an interactive SSH session, like moderated SSH sessions, tsh puts the terminal in to raw mode. In raw mode, a \n only moves the cursor down a line, not back to column 0. To fix this we have to use \r\n. This doesn't affect cooked-mode terminals.

Before change:

Teleport > Please tap your MFA key
If browser window does not open automatically, open it by clicking on the link:
                                                                                http://127.0.0.1:62258/d8c64b1f-3454-4027-b75b-bab6a0688234

Teleport > Received MFA presence confirmation

After change:

Teleport > Please tap your MFA key
If browser window does not open automatically, open it by clicking on the link:
 http://127.0.0.1:63911/5aa94a86-f4c3-4986-911a-47187a6929ad

Teleport > Received MFA presence confirmation

Manual Test Plan

Test Environment

Teleport e running locally with moderated sessions enabled.

Test Cases

• Formatting is fixed in a moderated session (raw mode)
• Formatting is unaffected in regular sessions (cooked mode)

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[danielashare]

@claude review once

[backport-bot-workflows]

@danielashare See the table below for backport results.

Branch	Result
branch/v18	Failed