Add username support for Ghost (hosted blogs)

[TedTschopp]

Ghost (hosted) username / blog handle validation

Category: creator

Goal: Allow checking for Ghost-hosted blog handles where Ghost provides a *.ghost.io subdomain.

Notes:

• Hosted Ghost blogs often live at https://{blog}.ghost.io/.
• Self-hosted Ghost instances will not be covered by this issue; focus on the official hosted variant.

Logic (to confirm):

• For https://{blog}.ghost.io/:
  • 200 → blog exists (Taken)
  • 404 / DNS failure → likely Available (or Error, depending on behavior)

Implementation notes:

• Add creator/ghost.py.
• Implement validate_ghost(username: str).
• Use status_validate() if status codes are consistent; otherwise fallback to generic_validate().

[Kushmanmb]

Kushmanmb