Add hints examples to the playground

Four examples under a new Hints group: basic beacons, the twelve beacon
anchor points, localStorage-backed dismissal persistence, and hints
coexisting with a tour (with a Take the tour button added through a hint
popover's onPopoverRender).

The playground imports the library from source, so driver.js/hints is
aliased to src/hints.ts in both the astro config and tsconfig. The
subpath alias is declared before the driver.js one because aliases match
on prefix.