fix(brain-sync): secret scanner now catches Bearer-prefixed auth tokens in JSON

The bearer-token-json regex value charset was [A-Za-z0-9_./+=-]{16,},
which does NOT permit spaces. Real HTTP auth headers embed the scheme
name with a literal space — "Bearer <token>" — so the value portion
actually starts with "Bearer " and the existing regex couldn't match.
Result: any JSON blob containing "authorization":"Bearer ..." would
slip past the scanner and sync to the user's private brain repo with
the bearer token inline.

Added optional (Bearer |Basic |Token )? prefix in front of the value
charset. Now matches the common auth-scheme forms without broadening
the matcher to tolerate arbitrary whitespace (which would false-positive
on lots of benign JSON).

Verified against 5 positive cases (bearer-in-json, clean bearer, apikey
no-prefix, token with Bearer, password no-prefix) + 3 negative cases
(too-short tokens, non-secret field names like username, random JSON).

This closes the P0 security regression first noticed during v1.12.0.0
/ship. brain-sync.test.ts now passes all 7 secret-scan fixtures.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

bin/gstack-brain-sync

@@ -88,7 +88,12 @@ patterns = [
     ('pem-block', re.compile(r'-----BEGIN [A-Z ]{3,}-----')),
     ('jwt', re.compile(r'\\beyJ[A-Za-z0-9_-]{10,}\\.[A-Za-z0-9_-]{10,}\\.[A-Za-z0-9_-]{10,}\\b')),
     ('bearer-token-json',
-     re.compile(r'\"(authorization|api[_-]?key|apikey|token|secret|password)\"\\s*:\\s*\"[A-Za-z0-9_./+=-]{16,}\"',
+     # JSON-embedded auth headers. The optional Bearer/Basic/Token prefix
+     # matters: real auth values include a literal space after the scheme
+     # name, but the value charset below does not include spaces, so
+     # without the optional prefix every Bearer token in a JSON blob slips
+     # past the scanner.
+     re.compile(r'\"(authorization|api[_-]?key|apikey|token|secret|password)\"\\s*:\\s*\"(Bearer |Basic |Token )?[A-Za-z0-9_./+=-]{16,}\"',
                 re.IGNORECASE)),
 ]
 text = sys.stdin.read()