alpha-linux-v0.1

fix(web): never store the files to print

Bugs:

- The service worker cached every same-origin GET response, not only the
  app's own files, so other requests ended up stored on disk.
- Files shared from other apps were written to a cache until the page read
  them; if the page never read them, they stayed there.

Now only the app shell (and the versioned pdf.js library) is cached.
Shared files are kept in the service worker's memory and handed to the
page with postMessage. The old shared-files cache is deleted on update.
Files opened, dropped or pasted were never stored and still aren't.

Changes made by Claude (Claude Code).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>