Validate synthetic value alignment during construction

[GG-O-BP]

Summary

• Synthetic list_attribute/list_text_template/list_expression/association builders silently returned undefined values when parallel value lists were shorter than the item list, crashing chart/grid consumers later.
• Constructors now validate one-value-per-item alignment and fail immediately with a descriptive error (function name, expected/actual counts) while preserving every public signature and the aligned-input behavior.
• New synthetic contract tests cover aligned construction across all four builders and mismatch rejection.

Fixes #13

Verification

• gleam test --runtime bun — 20 passed.
• ./scripts/verify.sh inner mendraw — passed.
• ./scripts/check-all.sh — passed.
• pre-push verify.sh final — passed on retry (family checks, widget build, Lustre E2E, Mendix full E2E); first attempt hit a transient Hex API rate limit.