Record installation on Mac, Windows, and Ubuntu

[rafiki270]

Summary

• Document installation and launch on the Mac, Windows, and Ubuntu machines.
• Add package installation instructions and record Ubuntu's installed AppArmor user-namespace sandbox behavior.
• Distinguish successful ChatterBox installation from existing Ubuntu kernel/DKMS package errors and remaining upgrade/signing gates.

Testing

• Documentation lint passed.
• Mac: installed bundle matched the tested artifact; native UI showed Connected from /Applications/ChatterBox.app.
• Windows: NSIS installer exited 0, Start menu shortcut and installed executable verified, app processes running in the active desktop session.
• Ubuntu: rebuilt from current application source, DEB registered as installed, desktop app running with sandboxed renderer (NoNewPrivs: 1, Seccomp: 2).
• All three installed apps passed authenticated board reads and SQLite integrity checks. No test data inserted into their real boards.
• Ubuntu apt returned 100 for pre-existing applespi DKMS/kernel failures; ChatterBox itself configured and launched successfully.
• Upgrade, uninstall, signing, notarization, and store publication were not tested.