Closes#1738. Four concrete fixes surfaced by the savings-goals
audit + #1737 universal checklist:
1. Focus ring (WCAG 2.4.7). `base.css` had
`focus-visible:outline-gray-900` which is **1.07:1** against the
primary button's gray-900 background — invisible. Widen to
`outline-2 outline-offset-2`, place outline outside the button
via offset, and add a dark-mode `outline-white` so the ring is
always visible against the page chrome regardless of the button
surface.
2. Touch target (WCAG 2.5.5). Icon-only buttons at the default
`:md` size were `w-9 h-9` = 36×36, below the 44×44 enhanced
target. Bump `md.icon_container_classes` to `w-11 h-11` and
`lg.icon_container_classes` to `w-12 h-12` to keep the size
scale intact. `sm` stays at 32×32 (already passes WCAG 2.5.8
AA's 24×24 minimum; intentional compact-density variant).
3. Default button type. `content_tag(:button, ...)` inherits the
HTML default `type="submit"`, so a DS::Button rendered inside a
form steals Enter-key submission from the first text input
(reproducible in the form stepper). Default to `type="button"`
in the non-`href` branch; existing form submitters pass
`type: "submit"` explicitly and continue to work. The `button_to`
(href) branch keeps the submit default because button_to wraps
its own form.
4. Icon-only accessible name. Icon-only buttons render no text
node, so AT users hear "button" with no name. Derive a
humanized aria-label from the icon key (e.g. `icon: "more-horizontal"`
→ `aria-label="More horizontal"`); explicit
`aria: { label: }` on the caller still wins. Soft fallback —
callers should still pass meaningful labels for richer copy.
Plus: replace the stale `fg-white` icon class on the destructive
variant with `text-inverse` (the `fg-*` namespace was deprecated
in #1626 so `fg-white` resolved to nothing; the icon was using its
helper-default color rather than the white the design intended).
Out of scope:
- Menu avatar trigger (custom 36×36 button bypassing DS::Button) —
belongs to #1743 DS::Menu audit.
- DS::FilledIcon `lg` size container (decorative, not interactive)
— belongs to #1742.
