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/entitlements.plist

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<!-- Hardened-runtime entitlements for FieldCraft. Deliberately empty: the app is pure Rust, loads
+     no unsigned code, needs no JIT and is not sandboxed (it opens files by path, from the command
+     line and drag-and-drop). Add an exception here only with a reason in a comment. -->
+<plist version="1.0">
+<dict>
+</dict>
+</plist>