fix: ensure messageBox and Toolbox are not visible to unauthorized users in read-only room

[SinghaAnirban005]

Brief Title

Unauthorized Users in Read-Only Channels Can Access Message Toolbox and React with Emojis

Acceptance Criteria fulfillment

• [x] Revise the canSendMsg global state
• [x] Ensure that users in read-only channels cannot access the message toolbox.

Fixes #868

Video/Screenshots

https://github.com/user-attachments/assets/5c3709ff-f0bb-4d17-81fc-e0dfdc0e5782

PR Test Details

Note: The PR will be ready for live testing at https://rocketchat.github.io/EmbeddedChat/pulls/pr-874 after approval. Contributors are requested to replace <pr_number> with the actual PR number.