refactor(frontend): IconButton folded into Button

[Kadrian]

Design-system prep, step 7: IconButton folded into Button

Stacked on #4006. IconButton and BasicButton are gone; the 93 icon buttons are Buttons with an Icon child, so one component covers every button in the app.

<Button intent="tertiary" aria-label={t("common.delete")} onPress={onDelete}>
  <Icon icon={faTrash} />
</Button>

• frame became intent="secondary", everything else tertiary; active → aria-pressed, red → text-red, tiny/bare/tight → size="sm", large → lg; bgHover, light, iconColor and the hand-tuned paddings are gone, the fixed sizes own the geometry
• icon-only buttons inside a TooltipTrigger got the tooltip text as aria-label (40 sites); the remaining 20 icon-only buttons without a tooltip still lack an accessible name
• onClick → onPress; the stopPropagation calls went, press events don't bubble
• the select boxes' reset and toggle buttons, the snack message's close button and the wrappers (HistoryButton, PreviewButton, QueryResultHistoryButton, DownloadButton) sit on Button
• excludeButton and the negate action show red when pressed via aria-pressed:text-red
• controls line up at 30 px: text, number and date inputs, the search fields and the select boxes have a fixed height (36 px on the login page, like its large button); the small remove and clear buttons (×) are sm

Not pretty, but only until the next PR merges: the editor-v2 toolbar and the previous-queries list are sm now; the download button that was large is lg.