fix(instrument-utils): leave measures on unrevealed dynamic questions out of the results summary

[joshunrau]

Closes #1098

What changed

Two fixes to computeInstrumentMeasures, which only feeds the results summary (after submission and on the datahub record page). Exports, tables and graphs use the measures the API stores, so they are unaffected.

1. Const measures are read through their ref. The summary looked up a const measure's value and label by its key in instrument.measures rather than by measure.ref, which is what the API stores. A measure keyed apart from its field showed another field's value, showed "NA", or threw a TypeError when the key named no field. To index data by ref without a suppression, the measures record is widened to InstrumentMeasures<any, Language>. Under an interactive instrument's Json data type, ConditionalKeys turns ref into a union of Json[] members. The widening also makes the @ts-expect-error on the computed branch unnecessary.
2. Measures on dynamic questions the respondent never saw are left out. If a const measure's field is kind: 'dynamic' and its render(data) returns null (the new isFieldHidden in form.ts, which builds on getFormFields), the measure is skipped quietly, whether or not it has a label. Before, a labeled measure showed "Label: NA", and an unlabeled one disappeared only because its label lookup failed, which also logged a spurious console.error. An optional static field the respondent saw and skipped still shows "NA".

The InstrumentSummary test fixture gets content: {}: the summary now reads a form's content for its const measures, and real form instruments always have one.

Verification

• Unit (instrument-utils): src/__tests__/measures.test.ts covers a measure keyed apart from its ref, a labeled measure on a hidden dynamic field (absent) and on a revealed one (present), an unlabeled hidden one (absent, with no console.error), and an unanswered static field (still present). src/__tests__/form.test.ts covers isFieldHidden. Each new test failed before its fix.
• E2E: testing/src/specs/playground.spec.ts adds two cases for a form whose pet-name question appears only when "Has Pet" is true: the name's measure is absent when the toggle is false and listed when it is true. With the fix reverted, the "absent" case fails with Expected: 0, Received: 1.
• pnpm lint passes (34/34). pnpm test passes (1585/1585). On chromium, the playground spec passes 14/14, and instrument-completion, form-block, form-reset and subject-detail pass 21/21.

Not run: the full pnpm test:e2e suite, and the firefox project. Neither new e2e test is @smoke.

Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com