Add check-digit algorithms (Luhn, Verhoeff, Damm, ISO 7064 MOD 97-10)

[JE-Chen]

Summary

Round-11 (research-driven). pii_text detects card/IBAN shapes by regex and data_quality does regex validation, but nothing computed or verified a check digit. This adds the shared arithmetic engine behind most real-world identifiers and the primitive that a future identifier_validate (IBAN/ISBN/EAN/card) builds on.

Layers

• Headless core: je_auto_control/utils/checksum/checksum.py — luhn_validate/luhn_check_digit, verhoeff_*, damm_*, mod97_10_validate/mod97_10_check_digits. Pure stdlib (integer arithmetic; small embedded Verhoeff/Damm tables), no PySide6, pure functions.
• Facade: all 8 re-exported + __all__.
• Executor: AC_checksum_validate → {valid}, AC_checksum_digit → {check_digit}, via explicit scheme-dispatch dicts (luhn/verhoeff/damm/mod97).
• MCP: ac_checksum_validate / ac_checksum_digit.
• Script Builder: two CommandSpecs under Data.

Tests / docs

• test/unit_test/headless/test_checksum_batch.py — 9 headless tests (Luhn 79927398713 + card, Verhoeff/Damm transposition catching, MOD 97-10 IBAN vector + 2-digit append, round-trips, unknown-scheme error + wiring + facade).
• EN/Zh feature docs v115_features_doc.rst + toctrees; 3 WHATS_NEW changelog entries.

[codacy-production]

Not up to standards ⛔

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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