Same shape of bug as the refreshToken duplication: the regex that strips
access_token / Bearer headers from logged HTTP bodies existed in three
near-identical copies (HasSocialHttpClient trait, TokenRefreshClient,
SocialPublishException), drifting subtly — SocialPublishException was
missing the JSON "token" pattern.
Extracts a TokenRedactor::redact(string) helper and routes all callers
through it. Adding a new token format now means one regex in one file.
