Strip formatting when pasting into SMS templates

Fix SMS template creation so pasted text is preserved and pasted formatting is stripped instead of causing the content to disappear or fail.

Transcript Context

Catherine reported that when creating the new SMS templates, pasting text into the editor did not work reliably and could appear blank even after saving. During the discussion, Chris and Ryan suspected the editor was trying to preserve source formatting instead of stripping it, which caused the paste behavior to fail.

The expected behavior is that users should be able to paste normal text into an SMS template without needing special paste commands, and any unsupported formatting should be removed automatically.