JS walker computes styles for form controls that never use them #106

Found in the review of the capture-live-form-state branch.

formControlState() in ElementToSemanticEvents.kt calls isMasked() — a getComputedStyle — for every <input>, including checkbox / radio / submit / hidden / file, where formControlAttributes never reads masked.

Scenario: a search page with hundreds of filter checkboxes pays one computed-style lookup per checkbox, all discarded.

Fix: check the input type first, or compute masked lazily (e.g. pass a () -> Boolean, or let FormControls.kt expose which types need it).