The existing OpenAI pattern sk-[a-zA-Z0-9]{20,} never matches real
Anthropic keys: their sk-ant-api03-... format contains hyphens, which
break the character class before reaching the 20-char threshold. Keys
from the fastest-growing Claude Code user base slipped through the scan.
Adds a dedicated sk-ant-[a-zA-Z0-9_-]{20,} pattern (checked before the
OpenAI one) and extends the staged-secrets test with a realistic
Anthropic key fixture.