Complete Issue #8 CLI and provenance semantics

[rastagan-git]

Summary

• reserve Retrieved At for actual provider or cached representations, leaving skipped and pre-response failures blank
• make --no-odor skip PUG-View and omit the five odor-only output columns without altering pre-existing input columns
• add python -m aromanexus with console-equivalent help, version output, and exit codes
• add opt-in --existing-cas-column confirmation for non-CAS queries, with explicit confirmed, conflict, and invalid outcomes
• keep partial PubChem results conservative: accept positive CAS confirmation only, otherwise report not_evaluated
• include every standard PubChem output in XLSX width preflight so failures occur before provider calls
• synchronize the English/Chinese READMEs and the curate-aroma-data skill contract

Conservative CAS behavior

The optional existing CAS is never treated as authoritative by itself:

• a checksum-valid value present among returned candidates becomes input_cas_confirmed
• a valid but absent value becomes input_cas_conflict
• an invalid nonblank value becomes input_cas_invalid
• blank values retain the existing unique, multiple, and missing rules
• active output-column collisions are rejected before provider access
• candidate lists and provenance remain unchanged

Validation

• python -m pytest: 87 passed
• python -m ruff check .: passed
• python -m ruff format --check .: passed
• project skill validation: passed
• real sample-workbook inspection: passed
• isolated wheel build: passed; wheel contains aromanexus/__main__.py
• two focused read-only code-review passes: no remaining actionable findings

Completes sections 2–5 of #8. XLSX fidelity and --sheet support were delivered by #9.

Closes #8