Add a check for stale generated sample fixtures

Several checked-in sample_std.json fixtures drifted from the current converter output even when the semantic conversion was sound. A repository check should catch this earlier.

Acceptance criteria:

• Add a script or test that regenerates committed samples from sample_raw.json/sample_atif.json and reports drift.
• Make the check usable locally and in CI.
• Keep the check deterministic and skip datasets with unavailable optional dependencies in a clearly reported way.
• Document how to refresh fixtures when intentional converter changes occur.

Start by locating the converter and the committed sample_raw.json, sample_atif.json, and sample_std.json fixtures, then run the existing sample-generation or test workflow. Add a deterministic local and CI check that reports drift, clearly skips unavailable optional dependencies, and document the intentional fixture-refresh process. Done means stale fixtures fail the check while valid optional-dependency skips are visible.