Testnizer v1.4.15

v1.4.15

macOS in-app auto-update now actually works, the update panel stops claiming
"you're up to date" before it has checked, and the welcome screen gained the
version number plus a working About menu.

• macOS auto-update (for real): now that builds are signed and notarized
  (v1.4.13+), the in-app Download & Install flow works on macOS too — the
  old block that forced macOS users to a manual download has been removed. The
  manual download link remains as a fallback if an install can't complete.
• Honest update status: the update panel no longer shows a green "you're up
  to date" before any check has run. Opening it now runs a check automatically,
  shows a neutral prompt until the result is in, and only reports "up to date"
  once a check confirms there's no newer version.
• About works on the welcome screen: selecting Testnizer → About
  Testnizer from the menu now opens the About dialog even before you've signed
  in / chosen a profile (previously it did nothing on the first screen).
• Version on the welcome screen: the first-run screen now shows the build
  version.
• Turkish polish: the update-panel Turkish strings now use correct
  diacritics (e.g. "Güncelsiniz" instead of "Guncelsiniz").

Tests: updater event→status mapping (incl. the new not-available → up-to-date
split), the macOS in-app Download path, and the welcome-screen version badge —
unit suite now at 1715.