fix: prevent errant body string on title edit

[asajjad2]

What are the relevant tickets?

#8681

Description (What does it do?)

This change aligns the legacy discussion “Edit Post” behavior with the “New Post” form by preventing the Enter key in the title input from inserting markdown (strong text as observed in the issue) into the body. It adds a keypress handler scoped to the edit form to ignore Enter on non-editor inputs, preserving normal behavior within the body editor.

How can this be tested?

1. Navigate to an LMS course discussion page → open any thread you own → click edit on the post.
2. Click into the Title input.
3. Press Enter and verify nothing happens:
   • The form does not submit
   • focus remains in Title
   • body is unchanged
   • no “strong text” appears in the editor preview/body.
4. Press Tab to move focus to the body (editor textarea) and type some text, then press Enter.
   Expected: normal editor behavior (a newline is inserted). The Enter key is not blocked inside the body editor.
5. Click Update post to save and verify no unintended markdown was inserted in the title or body.

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[Anas12091101]

LGTM 👍

[asajjad2]

@pdpinch this PR is approved and ready to be merged.

[pdpinch]

👍 assuming tests pass