Reactions (emoticons) after import from Slack show all up as `name`.

Description:

Steps to reproduce:

1. Import Slack archive: users and channels
2. Fix MongoDB so imported messages show up in channels (otherwise channels look empty) as currently Slack import does not work properly at all. Multiple options:
   • manually run commands in mongosh: https://github.com/RocketChat/Rocket.Chat/issues/37058#issuecomment-3342623466
   • wait for #37805 to be update with this fix (or a better one): https://github.com/RocketChat/Rocket.Chat/pull/37805#issuecomment-3743637660
   • Get the database migraton from https://github.com/RocketChat/Rocket.Chat/pull/38090 running after the import to fix MongoDb database (same commands ran as in manual mongosh step.
3. Go to a channel with messages that have reactions. All reactions have the name name and thus the emoticons do not show up.

Expected behavior:

I expect that reactions show up with their emoticons.

Actual behavior:

All reactions have the name name and thus the emoticons do not show up.

Server Setup Information:

• Version of Rocket.Chat Server: 7.13.2
• Operating System: Ubuntu
• Deployment Method: Docker
• Number of Running Instances: 1
• DB Replicaset Oplog: iredTiger (oplog Enabled)
• NodeJS Version: v22.16.0
• MongoDB Version: 6.0.13

Client Setup Information

• Desktop App or Browser Version: In all browsers
• Operating System: On all operating systems

Start by reproducing the Slack archive import and inspecting the reaction data shown in a channel after the MongoDB fixes described in the issue. Trace how imported messages and their reactions are represented, then verify that imported reactions display their emoticons rather than name.