`aria-*` boolean attributes serialize as the empty string

Lies design/v2/follow-up-issues.md und untersuche den Base-Serialisierungspfad für aria-Attribute im 2.0-Zweig. Führe die golden HTML suite aus und prüfe die betroffenen Katalog- und Komponenten-Snapshots, einschließlich Breadcrumb-Trennzeichen, Ellipse, CommandInput und dekorativer SVGs. Erledigt ist die Aufgabe, wenn aria-Boolesche Werte wie festgelegt als "true" oder "false" gerendert werden, die 2.0-Snapshots neu aufgezeichnet wurden und ihr Diff geprüft wurde.

• Where: the components that pass a boolean under the aria hash:
  aria: {hidden: true} in BreadcrumbSeparator, BreadcrumbEllipsis and
  PaginationEllipsis (also reached through DataTablePagination),
  aria: {disabled: true} in BreadcrumbPage, aria_expanded: true in
  CommandInput. The breadcrumb, pagination, data_table and command
  snapshots carry aria-hidden="", aria-disabled="" or aria-expanded="".
  Components that pass the String "true" — InputOtpSlot,
  NativeSelectIcon, AlertDialogContent — already serialize correctly and
  are not affected.
• Effect: the ARIA value grammar accepts true/false/undefined; an
  empty string is invalid and browsers resolve it as not set. The breadcrumb
  and pagination separators and ellipses are therefore exposed to assistive
  technology, "current" breadcrumb items are not announced as disabled, and the
  command input's expanded state is unset. This is Phlex's serialization of
  true under a nested hash (a bare attribute), so any component that passes
  a boolean there is affected — five today.
• Fix: pass "true" (a String) for aria-* attributes, or add a
  serialization rule in Base that stringifies booleans under the aria
  key; re-record (on the 2.0 line) everything that changes and review the diff.
• 2.0 note: spec §4.3 currently preserves this behaviour for parity
  (true → ""). The right 2.0 behaviour is aria-x="true"; decide it
  explicitly and let the re-record (on the 2.0 line) show the blast radius.

Surfaced by the golden HTML suite (PR #536), which pins what 1.6 renders today — this defect included. Per maintainer decision (2026-09-19) main stays as is: this is addressed on the 2.0 line, and the golden snapshot that pins it is re-recorded there with the diff reviewed.

Source: design/v2/follow-up-issues.md.