[bug]: Default focus ring (ring-ring/50) is under 3:1 contrast in light and dark #12521

Describe the bug

Focus on Button, Input and Select is a 1px border-ring plus a 3px ring-ring/50. In the default neutral theme:

• Light: --ring is oklch(0.708 0 0) (about #a1a1a1). The border is 2.58:1 on white, and the 50% ring composites to about #d0d0d0, which is around 1.5:1. On outline buttons, inputs and selects the border changes from #e5e5e5 to #a1a1a1, a 2.05:1 change.
• Dark: the strongest change is 2.47:1 on Input and Select, and 1.88:1 on outline buttons (the outline border doesn't change at all in dark mode, see [bug]: Outline Button's focus border is overridden in dark mode (no visible focus in forced colors) #12516).

In light mode, no pixel of the focus indicator reaches a 3:1 change against its unfocused state on any variant or size. That fails WCAG 2.4.13 Focus Appearance (AAA), and 1.4.11 Non-text Contrast (AA) as it's usually applied to focus indicators.

Using the ring at full opacity isn't enough on its own, because --ring itself is 2.58:1 on white. A darker light-theme --ring, for example oklch(0.556 0 0) (about #737373, 4.7:1 on white), at full opacity would clear 3:1.

Related but different: #12344 (invalid rings hide focus) and #11320 and #12343 (components with no focus style at all).

Affected component/components

Button (all variants), Input, Select trigger, and the other components that use focus-visible:ring-ring/50. Checked in base-nova and radix-nova. new-york-v4 uses the same classes and tokens.

How to reproduce

1. Fresh init -d, then add button, input and select.
2. Tab to an outline Button or an Input on a white background.
3. Measure the focus border and ring colors against the background. DevTools' color picker shows the ring as semi-transparent, so composite it first.

Codesandbox/StackBlitz link

None (default install).

Logs

System Info

shadcn 4.23.0, Tailwind CSS 4.3.3. Chrome and Safari on macOS.

Before submitting

• I've made research efforts and searched the documentation
• I've searched for existing issues