detect-secrets flags realistic Google-style IDs as Base64 High Entropy Strings

Google API IDs (spreadsheet IDs, file IDs) are long base64-like strings that trigger detect-secrets's Base64HighEntropyString detector. This blocks commits containing realistic testdata JSON fixtures. Using pragma: allowlist secret per-line is possible but noisy across many fixtures.

Use simple placeholder IDs (e.g. spreadsheet-id-001, file-001) in test fixtures instead of realistic-looking Google-style IDs to avoid false positives from detect-secrets.