Java SDK: Let a native Java Dag set one queue for all its tasks

[jason810496]

Why

Every task of a native Java Dag runs on the Java coordinator, so each one needs a queue that [sdk] queue_to_coordinator routes there. Airflow's Dag has no queue setting, so authors had to repeat the same queue on every task. The Go and TypeScript SDKs already take a Dag-level queue; this gives Java the same.

What changes

queue can be set once on the Dag, in both styles. Each task inherits it, unless the task sets its own queue.

// Annotation style.
@Airflow.Dag(id = "etl", schedule = "@daily", queue = "java")
public class Etl { ... }

// Interface style.
var dag = new DagDef("etl").config("queue", "java");
dag.task("extract", Extract.class);                           // runs on "java"
dag.task("heavy", Heavy.class).config("queue", "java_large"); // its own queue wins

• Same rules as Go and TypeScript: conditions, switches and TriggerDagRun tasks inherit the queue too, a task's own queue always wins, and the queue is never written on the serialized Dag itself.
• The native Java examples now set queue = "java", which the README's setup already routes to the Java coordinator.

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Was generative AI tooling used to co-author this PR?

• Yes, with help of Claude Code Opus 5.5 following the guidelines

[FrankYang0529]

Overall LGTM.