[CLNP-6499][fix]: improve wording for mention limit error message

[sf-tyler-jeong]

Fix inaccurate wording in the mention limit warning message.

Problem:
When a user reaches the mention limit (default 10) and types @, the warning message displayed was misleading:

• Before: "You can mention up to %d times at a time."

Fix:
Updated the message to accurately describe the constraint:

• After: "You can have up to %d mentions per message."

Fixes CLNP-6499

Changelogs

• Fixed inaccurate wording in mention limit warning message from "mention up to %d times at a time" to "have up to %d mentions per message"

Checklist

• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• Public components / utils / props are appropriately exported
• I have added necessary documentation (if appropriate)

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