chore: rename to ObjectOS One, @objectos/server v6.0.0, add app icons

 apps/objectos-one (reserve 'desktop' for future thin client)
 apps/objectos/one.mjs
 scripts/build-one.sh
 .github/workflows/one.yml (tag: one-v*)
 6.0.0 (align with @objectstack/*)
 6.0.0
 objectos-one (lib: objectos_one_lib)
- Generate stacked-objects app icons for all platforms (icns/ico/png)
- Ignore .objectstack/ runtime data

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: hotlong