fix(web): restore pointer cursor on buttons

[xbsheng]

Fixes #594.

What was wrong

Every <button> in web/ stayed on the browser's default arrow cursor when hovered — the locale switcher and dark-mode toggle in the header are the most visible, but the same applied to the Compare/Diff tabs, the simulator and visualization playback controls, and the Design Decisions collapsibles.

Cause: web/ is on Tailwind CSS v4, whose preflight no longer contains the v3 rule button, [role="button"] { cursor: pointer }. Buttons therefore fall back to cursor: default, while <a> (nav links, GitHub icon) still gets pointer from the UA stylesheet — hence the mixed appearance in the same header row.

Confirmed against the production bundle: the only cursor declaration in the deployed CSS is .cursor-pointer, used exactly once (web/src/app/[locale]/page.tsx:219).

Fix

Restore the rule once in web/src/app/globals.css, rather than adding cursor-pointer to each of the 18 buttons:

button:not(:disabled),
[role="button"]:not(:disabled) {
  cursor: pointer;
}

:not(:disabled) is deliberate: step-controls.tsx and simulator-controls.tsx have disabled buttons, and those should keep the default cursor.

Verification

• npm ci && npm run build in web/ succeeds, and the emitted CSS chunk contains button:not(:disabled),[role=button]:not(:disabled){cursor:pointer}.
• Diff is one file, CSS only; no component or generated-data changes.

AI disclosure

I used an AI coding agent to trace the cause and draft this patch. I read the full diff, ran the build, and stand behind the change.