fix: recover installers from stale uv cache

[EvanProgramming]

Summary

• retry POSIX and PowerShell release installs with uv --no-cache when the normal cached install fails
• apply the same recovery to the in-app package-manager update path
• add a disposable fake-uv regression that reproduces the first-failure/uncached-retry flow

Validation

• sh -n install.sh
• focused uncached-retry and installer distribution tests
• Python compile checks
• git diff --check
• Fixes [P1] Installer should recover from incomplete uv cache archives #154