fix(ui): draw one focus ring, not two

src/index.css already declared "one visible, consistent focus treatment",
but shadcn's primitives ship a `focus-visible:ring-[3px]` of their own, so
every button and input actually drew two: a soft translucent halo hugging
the border, then a hard 2px outline 2px further out.

The global rule is the one that stays, because it also covers the links and
bare table buttons that never go through a primitive. The rings come out of
button.tsx and input.tsx instead.

Its `border-radius: 2px` goes too. That was squaring the corners of every
control with no radius utility of its own — the rule-history triggers in
Settings measured `rad=0`, so a focused one drew a sharp rectangle. The
outline now follows each element's own radius.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/components/ui/input.tsx

@@ -9,8 +9,9 @@ function Input({ className, type, ...props }: React.ComponentProps<"input">) {
       data-slot="input"
       className={cn(
         "h-9 w-full min-w-0 rounded-md border border-input bg-transparent px-3 py-1 text-base shadow-xs transition-[color,box-shadow] outline-none selection:bg-primary selection:text-primary-foreground file:inline-flex file:h-7 file:border-0 file:bg-transparent file:text-sm file:font-medium file:text-foreground placeholder:text-muted-foreground disabled:pointer-events-none disabled:cursor-not-allowed disabled:opacity-50 md:text-sm dark:bg-input/30",
-        "focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50",
-        "aria-invalid:border-destructive aria-invalid:ring-destructive/20 dark:aria-invalid:ring-destructive/40",
+        // The focus outline is src/index.css's, for the whole app at once —
+        // see the note in button.tsx.
+        "aria-invalid:border-destructive",
         className
       )}
       {...props}