fix(livechat): prevent whitespace-only values in Name, Description and Message

[Codersintu]

Fixes RocketChat#38512

Problem

Whitespace-only values were accepted in Name, Description, and Message fields.

Solution

• Added validation to prevent leading/only whitespace
• Treated whitespace-only strings as empty

Result

Users cannot save invalid triggers.

Testing

• " " → rejected
• "hello world" → accepted