Enforce top-level additionalProperties: false in load_param_table_yaml()

[Copilot]

load_param_table_yaml() validated columns[*] entries but silently ignored unknown top-level keys, allowing typos like colums: to go undetected despite schemas/param-table-schema.json specifying additionalProperties: false at the top level.

Changes

• tools/create_param_appendix.py: After loading the YAML, compute the set difference against {"columns", "$schema"} and fatal() if any unexpected keys are present.

allowed_top_level_keys = {"columns", "$schema"}
unexpected_top_level_keys = sorted(set(data.keys()) - allowed_top_level_keys)
if unexpected_top_level_keys:
    fatal(
        f"Unexpected top-level properties in {pathname}: "
        f"{', '.join(unexpected_top_level_keys)}"
    )

A file with a key like colums: now produces a clear fatal error instead of silently proceeding with the columns: data.

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[Copilot]

Pull request overview

This PR tightens validation of the parameter table layout YAML consumed by tools/create_param_appendix.py, ensuring the YAML’s top-level shape matches the schemas/param-table-schema.json contract.

Changes:

• Added top-level key validation for the parameter table YAML, only allowing columns and optional $schema.
• Emit a fatal error when unexpected top-level properties are present.

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