Condition::ClassReference + lutaml-model migration plan (TODO 19)

[ronaldtse]

Summary

Implements TODO 19 from the cdd-data 2026-07-23 session.

Item 1: Condition grammar — ClassReference subclass (code)

IEC 62683 stores property conditions as bare class-reference sets like
{0112/2///62683#ACE132}, which Opencdd::Condition.parse previously
rejected. The workaround in Property#condition rescued ArgumentError
and returned nil — silently dropping the data.

This PR adds Opencdd::Condition::ClassReference per the approved
grammar:

condition       := expression | class_reference
expression      := identifier OP (literal | set)
class_reference := irdi | set
set             := "{" element ("," element)* "}"
element         := irdi | identifier

Files changed:

• lib/opencdd/condition.rb — new ClassReference subclass; parse
  dispatches bare IRDI / bare set to it. Malformed input (e.g.
  "no operator here") still raises ArgumentError.
• lib/opencdd/property.rb — removed the rescue ArgumentError;
  class references now parse instead of becoming nil.
• lib/opencdd/validator/condition_rule.rb — comment clarification;
  existing !parse(value).nil? already accepts ClassReference.
• spec/condition_spec.rb — 14 new cases (bare IRDI, bare set,
  satisfaction, round-trip, equality, cross-type comparison).
• spec/validator_spec.rb — 2 new R11 cases for class references.

Item 2: lutaml-model migration — full phased plan (docs)

Expands the TODO 19 Item 2 summary into a fully-decisioned plan with
all three user decisions applied:

1. Per-item + single-file layouts coexist (per-item default).
2. YAML default, JSON as format: override.
3. Multilingual fields as nested maps in YAML/JSON; flat only in Parcel xlsx.

Files added:

• TODO.final/19b-lutaml-model-migration.md — full plan for Phases
  2.1 (done) → 2.5, with files-to-change, acceptance criteria, risks,
  and how each decision shows up per phase.
• TODO.final/19-condition-grammar-and-lutaml-migration.md — pointer
  from the proposal summary to the detailed plan.

Pending-spec cleanup (drive-by)

• spec/database/public_api_coverage_spec.rb — find_by_name was
  perpetually skipped; added MDC_P004.en to the fixture's klass
  and wrote 4 real cases.
• spec/parcel/round_trip_matrix_spec.rb — removed the
  CDDAL→JSON→CDDAL placeholder; replaced with a comment deferring to
  Phase 2.5 (which makes the round-trip implementable).

Test plan

• bundle exec rspec spec/condition_spec.rb — 31 examples, 0 failures
• bundle exec rspec spec/validator_spec.rb -e "R11" — 4 examples, 0 failures
• bundle exec rspec (full suite) — 930 examples, 0 failures, 0 pending
• No new def to_h / from_h / to_hash introduced
• No AI attribution in commit message