Java: report progress and logs from an attached executor #594

Wire the Java executor's job-scoped operations to the side-channel from the core issue.

Java took the strictest line of the three SDKs: its executor holds no QueueBackend at all, so WorkerDispatchBridge already treats storage as absent. Two gaps follow from that, and both close the same way.

• Progress and task logs route JobContext → WorkerControl → NativeExecutor, mirroring how completeJob/failJob already resolve through the executor handle rather than through a queue.
• loadMetadata currently returns an empty map on an executor because it reads backend.getJobJson. It should read the metadata the job frame now carries, so middleware sees the same map it would in a worker.

MiddlewareDisables likewise takes its list from the job frame instead of the settings read it cannot perform.

Done when

ExecutorAttachTest asserts, against its socket scheduler: a handler reporting progress produces a progress frame; a published partial produces a task_log at level result; middleware sees the job's metadata; and a middleware named in the frame's disable list does not run.

Note that :compileTestJava is currently skipped in some environments, so state how the tests were actually executed.

Parent issue carries the rationale.