fix: allow hyphens and spaces in theme generator theme name

[Parth10P]

Fixes #4387.
The theme generator silently discards all changes when the theme name contains a hyphen (e.g. my-theme) or a space (e.g. cringe classic). This is caused by an overly restrictive regex in themeGeneratorValidation.js that only accepts [a-z] characters.

changes made

• Updated themeNamePattern in themeGeneratorValidation.js to allow lowercase letters, digits, spaces, and hyphens (while continuing to prevent them at the very start or end of the name).
• Added .trim() to the validation pipeline so that trailing spaces typed by users don't temporarily break the validator or pollute the generated output.

Screen.Recording.2026-03-18.at.7.mp4

[Parth10P]

@saadeghi is anything need's to be change or edits..?