ci: release-smoke - run a real Maven build instead of jbang/javac+java

Both smoke paths previously bypassed Maven: the native-runner legs used
jbang, the container-probe legs used a quiet dependency-plugin:copy +
raw javac/java. Output was a single terse line, nothing that looked
like an actual build.

Move Smoke.java into a standard src/main/java layout and add a
standalone .github/smoke/pom.xml (outside the root reactor) that
resolves the released zstd + native jars via -Dzstd.version/
-Dzstd.classifier and runs them with exec-maven-plugin. Vendor the
Maven Wrapper already used at the repo root so no leg needs a
preinstalled Maven - including inside the 8 container-probe images,
which now run the same `mvnw compile exec:exec` under their own JDK
instead of only executing a bare `java` command compiled on the host.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: dfa1

.github/smoke/.mvn/wrapper/maven-wrapper.properties

@@ -0,0 +1,3 @@
+wrapperVersion=3.3.4
+distributionType=only-script
+distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.16/apache-maven-3.9.16-bin.zip