Expand secret redaction patterns

[bug-ops]

Context

Security audit (2026-02-15) reviewed zeph-core/src/redact.rs and suggests adding additional API key prefixes to the redaction patterns.

Severity

Informational — current patterns cover major providers.

Suggested additions

const SECRET_PREFIXES: &[&str] = &[
    // ... existing patterns
    "AIza",          // Google API keys
    "ya29.",         // Google OAuth tokens
    "glpat-",       // GitLab PAT
];

Acceptance criteria

• New prefixes added to SECRET_PREFIXES
• Tests verify redaction of new patterns