Extend the accessible-name guard to <select> and <textarea>

[atomantic]

The repo-wide a11y guard ("gives every input an accessible name") currently inspects <input> tags only. <select> and <textarea> are outside its scope entirely, so a newly-added unlabeled dropdown or textarea passes CI silently.

Scope

• Extend the guard in the client a11y test to parse <select> and <textarea> opening tags with the same brace-aware logic already used for <input> — including the existing escape hatches: aria-label/aria-labelledby, an id targeted by an htmlFor in the same file, isNestedInLabeledFormField(), and isNestedInLabelWrappingComponent() (added in name the unlabeled inline form controls on the a11y sweep's high-value pages #4307).
• Extending it will surface a fresh backlog of pre-existing offenders. Seed a separate allowlist for them (mirroring PREEXISTING_INPUT_NAME_ALLOWLIST, tracked for migration the same way Add accessible names to pre-existing unlabeled input controls #4297 tracks the input one) so the guard lands green and the backlog burns down incrementally — do NOT mass-apply aria-label to clear it.

Why separate

Kept out of #4307 deliberately: that PR removed 20 entries from the input allowlist, and adding a whole new tag class in the same diff would have mixed a backlog burn-down with a backlog creation.

Refs #4156

[atomantic]

Shipped in #4325. Two calls made while implementing, recorded here so the burn-down is unambiguous:

• One shared allowlist (PREEXISTING_SELECT_TEXTAREA_NAME_ALLOWLIST) for both new tags, as the issue asked, but the anchor now carries the tag name (file|select|value=…). Without that, a <select> and a <textarea> in the same file with the same attribute set would exempt each other. The three existing input rows were re-anchored to the same format rather than keeping a second anchor shape alive.
• Per-tag tests rather than one merged rule, generated from a small table, so a failure names the tag and each backlog can burn down on its own schedule. All three still share one memoized scan per tag.

Seeded backlog: 62 <select> + 64 <textarea>. The input allowlist did not grow and no previously-passing control started failing.