RedAlert v1.2.3 - Linux launcher icon fix

Fix: Linux launcher showed cached placeholder icon

What was broken

On Linux, the v1.2.2 launcher entry referenced the app icon by absolute path
(Icon=/.../assets/icon.png). When that PNG was replaced in-place between
builds (e.g. swapping the placeholder for the branded shield), GNOME and many
other launchers kept showing the original cached image because their
thumbnail cache doesn't reliably invalidate on path+mtime alone.

What's fixed

• The app icon is now installed into the user's hicolor icon theme at
  ~/.local/share/icons/hicolor/256x256/apps/redalert.png on first run.
• The .desktop entry references it by themed name (Icon=redalert) instead
  of an absolute path. Themed icons go through the icon-theme cache, which is
  rebuilt on demand.
• Best-effort gtk-update-icon-cache and update-desktop-database calls
  nudge the desktop to pick up changes immediately.
• Falls back to the absolute-path form if the theme install fails for any
  reason.

Existing v1.2.2 installs

If you installed v1.2.2 and see the green-circle placeholder in your apps
launcher, just upgrade to v1.2.3 and run RedAlert once — it will install
the themed icon and rewrite the launcher entry. You may need to log out and
back in for GNOME's icon cache to release the old image.

Install (Linux x64)

1. Download RedAlert-1.2.3-linux-x64.tar.gz below.
2. Extract and run:

   tar -xzf RedAlert-1.2.3-linux-x64.tar.gz
   ./RedAlert-1.2.3-linux-x64/RedAlert

3. On first launch the config page (http://localhost:3847) opens automatically,
   and the launcher entry + themed icon are installed so you can start it from
   your apps menu next time.

Notes

• The Pikud HaOref API is geo-blocked to Israeli IP addresses.
• Tarball SHA-256: 0ade0074261f23b2403ff29aa759c3a301f30065028d5ac65dd84791d4b46d78
• No Windows-affecting changes — the v1.2.1 MSI is still the latest Windows build.