Flatpak packaging: desktop entry, MIME, distributable bundle

org.testium.Testium.yaml uses host Python/Lua only (no bundled interpreter).
build.sh exports a .flatpak bundle. README documents the install procedure.

package/flatpak/org.testium.Testium.desktop

@@ -0,0 +1,10 @@
+[Desktop Entry]
+Name=Testium
+GenericName=Test Sequencer
+Comment=YAML-based test sequencer and runner
+Exec=testium %f
+Icon=org.testium.Testium
+Type=Application
+Categories=Development;
+MimeType=application/x-testium;
+StartupNotify=true