fix: app cmd parsing, usage & tests

Note: the integration tests don't work due to ValidateApp still
attempting to validate the host key for the test app which doesn't
exist. This will be fixed in a future commit.

tests/integration/common.sh

@@ -2,6 +2,16 @@
 
 set -e
 
+create_server_app_recipe() {
+  ln -srf ../resources/testapp ~/.abra/servers/foo.com
+  ln -srf ../resources/testrecipe ~/.abra/recipes
+}
+
+clean_server_app_recipe() {
+  unlink ~/.abra/servers/foo.com
+  unlink ~/.abra/recipes/testrecipe
+}
+
 function init() {
   ABRA="$(pwd)/../../abra"
   INSTALLER_URL="https://git.coopcloud.tech/coop-cloud/abra/raw/branch/main/scripts/installer/installer"