Merge the two asset pages into one Vite build page

[arhimede]

bundle-static-modules.md and manage-assets.md documented the same pipeline and contradicted each other — one said Vite and npm run build, the other said the npm script copied images "as is". A reader who found the wrong one first got the 1.2.0 answer.

They are now one page, kept at manage-assets.md so existing links keep working, retitled "Assets and the Vite build" in the nav. Three further findings are fixed in the merged text:

• Destinations were wrong. viteStaticCopy sends fonts to public/fonts/ but images to public/images/app/. The old text said both were "copied as is", so a reader would write asset('images/logo.png') and get a 404. There is now a source-to-destination table and an asset() example for each kind, matching what the shipped layout already does.
• The Node prerequisite was too loose. "Node.js v20" is satisfied by 20.0 through 20.18, which fail the install. package.json declares ^20.19.0 || >=22.12.0, and that is now what the page says.
• The promised public cleanup does not happen. emptyOutDir: true sits at the top level of vite.config.js instead of under build, where Vite reads it, so it is ignored — and build.outDir lies outside root, which Vite will not empty without an explicit opt-in. The page now describes what the build actually does: it overwrites what it produces, stale files survive, delete the generated folders yourself if you need a clean result.

The last point is an upstream bug in dotkernel/light as well, tracked separately; this page can be revisited once that is fixed.

[arhimede]

@GeorgeCatalinStan please confirm this
also take a look at this
dotkernel/light#117