Adds `args_secret_warning(data)` to bcc_core — returns a warning string
when any arg positional value looks like a raw credential (token prefix,
value following a secret-named flag, or URL with embedded user:pass like
postgres://user:pass@host). `--flag=value` inline forms are intentionally
skipped (the flag name already labels the value).
Adds `secret_warn` QLabel in ServerEditor's stdio page; shown/hidden by
`_check_args()` on every field change, and cleared on deselect or
stdio→remote type switch. Non-blocking — save path is not touched.
Closes#1
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
AJ