packaging: macOS app and dmg, Linux tar.gz and AppImage, Windows zip

packaging/macos/package.sh builds FieldCraft.app (io.github.jyviko.fieldcraft, with icon.icns
and the layered Assets.car), signs it with a Developer ID and notarizes it when the
credentials are there and ad-hoc otherwise, and puts it on a drag-to-Applications dmg that
is mounted and checked; fieldcraft-cli goes in its own zip. packaging/linux/package.sh makes
an FHS tar.gz (binaries, .desktop entry, hicolor icons, licences) and an AppImage made with
appimagetool and the type 2 runtime at pinned, hash-checked releases.
packaging/windows/package.ps1 zips fieldcraft.exe and fieldcraft-cli.exe (static CRT,
checked PE headers and icon). Every package carries README.md, LICENSE-MIT, LICENSE-APACHE,
NOTICE and THIRD-PARTY-LICENSES.txt (#72).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

packaging/macos/README.txt

@@ -0,0 +1,13 @@
+Install FieldCraft
+
+Drag FieldCraft.app onto Applications.
+
+If this build is not notarized (the release notes say so), macOS blocks the first launch:
+right-click FieldCraft.app in Applications and choose Open, then Open again. Or run
+
+    xattr -dr com.apple.quarantine /Applications/FieldCraft.app
+
+Updating: quit FieldCraft, drag FieldCraft.app from this disk image onto Applications and
+choose Replace.
+
+The command-line tool, fieldcraft-cli, is a separate download (fieldcraft-cli-*-macos-*.zip).