[Feature Request] Suggest file name from first line when saving a new file

[knayak24]

Issue/Description:
When saving a file for the first time in COSMIC Edit, the Save dialog does not suggest a file name. It would be helpful if COSMIC Edit could automatically suggest a file name derived from the first line of the document and highlight it so the user can start typing to override the suggestion.

For example, using the first 5 words, similar to the behavior in GNOME Text Editor.

Expected Behavior:

• The Save dialog should pre-fill the filename field
• The suggested filename should be based on the first few words (e.g. first 5 words) of the first line
• The filename should be sanitized (spaces, special characters, etc.)

Other Notes:

• This behavior exists in GNOME Text Editor and feels intuitive