feat: add doctor and redact secret reports

[megamen32]

What changed

• adds git-private2public doctor
• checks Git, git-filter-repo, repository/config health, secret-rule tracking, pre-push hook, and source/target access
• redacts all matched credential values in scan/guard reports
• reports only type, path/blob, line, length, and a short SHA-256 fingerprint
• updates English and Russian docs

Safety

The previous report printed matched values. This PR removes that leakage path: reports no longer expose the credential they detected.

Tests

• 48 passed
• warnings treated as errors
• python -m py_compile passes
• git diff --check passes