fix(ui): stop kit buttons from shrinking below their label (flexShrink: 0)

Follow-up to the nowrap fix: MUI's default flexShrink:1 was still squeezing buttons in flex rows below their content width, so with nowrap the label overflowed its padding and touched the button edges (measured: '+ Přidat položku' was 96px wide for 98px of content). Adding flexShrink:0 keeps each button at its natural width (now 131px, full padding restored). Verified via DOM measurement + visual on the offer detail.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/ui/Button.tsx

@@ -14,11 +14,12 @@ export default function Button<C extends ElementType = "button">({
       variant="contained"
       color="primary"
       {...props}
-      // Keep labels on one line — flex layouts otherwise shrink a button and
+      // Keep labels on one line and at their natural width — in flex rows MUI's
-      // wrap its text onto two lines, making the button tall. Callers can still
+      // default flexShrink:1 squeezes a button below its content, so the label
-      // override via their own sx.
+      // either wrapped to two lines or (with nowrap) overflowed its padding and
+      // hit the edges. nowrap + flexShrink:0 keeps buttons crisp. Caller sx wins.
       sx={[
-        { whiteSpace: "nowrap" },
+        { whiteSpace: "nowrap", flexShrink: 0 },
         ...(Array.isArray(sx) ? sx : sx ? [sx] : []),
       ]}
     />