Ship hints as the driver.js/hints entry

Two separate vite runs rather than one multi-entry build. Multi-entry
splits the shared popover primitive into a chunk, which would make the
tour bundle depend on a second file and cost every existing user bytes
for a feature they may never use; it also merged both stylesheets into
driver.css. Standing the entries alone keeps driver.css byte-identical
to master and the tour bundle within ~120 bytes of it, and lets hints be
used without the tour. Importing both duplicates the primitive (~2KB
gzip), which is safe because the copies only handle their own popovers.

The hints run writes to dist-hints/ and the postbuild folds it into
dist/. That indirection is not incidental: vite-plugin-dts takes its
entry from package.json's `types` field when bundling, not from the lib
entry, so pointing it at hints emits the tour's API under the hints name
and overwrites dist/driver.js.d.ts. api-extractor rolls up the hints
declarations from an explicit entry instead.

hints/package.json is a resolution shim for legacy node10, which predates
`exports`; attw is green across node10, node16 ESM/CJS and bundler for
both entries. sideEffects marks only CSS, so bundlers can drop unused
code from either entry.

Sizes (gzip): tour 6.7KB unchanged in CSS and ~6.8KB in JS, hints 4.2KB
JS + 0.4KB CSS standalone.