Match required and optional form-control pseudo-classes #446

Parent: #257

Proven gap

The merged live-value slice implements :valid, :invalid, and :placeholder-shown, and the selector dependency compiler already records required mutations for :required/:optional. The matcher has no required or optional branch, so both selectors currently fall through as unsupported.

Focused implementation

• define which input, select, and textarea controls support the required state;
• match :required and :optional from the live element type and required content attribute;
• preserve the existing bounded required and type attribute invalidation routes;
• keep buttons, hidden/range/color and button-like input types, and unrelated elements outside the applicable set.

Deferred validation debt

This implementation-only slice intentionally skips browser/WPT/native correctness runs, performance, allocation, memory, lifecycle, scene/pixel, product, hosted checks, and CI monitoring. Those remain required before #257 product acceptance.

This child does not extend full constraint validation, range, checked/indeterminate, disabled/enabled, read-only/read-write, user-valid/user-invalid, form-owner, or reset behavior. It does not touch consolidation PR #76.