Add live CLI progress for long-running jobs

specs/cli.allium

@@ -57,6 +57,14 @@ rule MachineOutput {
     ensures: CliInvocation.exit_code.updated()
 }
 
+invariant LongRunningProgress {
+    -- Human-readable rebuild and render invocations stream localized progress
+    -- while metadata comparison, site validation, and page rendering run.
+    -- Interactive terminals update one bounded progress bar; redirected output
+    -- emits stable progress lines. JSON mode emits no interim text and includes
+    -- the same ordered progress history in its final envelope.
+}
+
 rule AirplaneGate {
     when: CliCommandExecuted(command)
     requires: CliInvocation.airplane