Package as a PWA

[steren]

With a few additions, this tool could become an "app"

• serve all assets from domain (https://github.com/simonw/tools/issues/2)
• implement a service worker to cache all files for offline access (here's one I wrote manually, but workbox is probably better)
• create a manifest file with an icon and name
• implement a share target for mobile devices
• implement a file handler

Example of manifest for an app that does all the above: https://github.com/steren/stereo-viewer/blob/main/manifest.json