build: silence reactor javadoc cross-link errors

Set detectOfflineLinks=false on maven-javadoc-plugin. The native and bom modules
have no Java sources, so reactor link detection created fake apidocs directories
and logged 'Error fetching link'. Disabling cross-linking removes the noise; the
zstd module's javadoc is self-contained.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: dfa1

pom.xml

@@ -131,6 +131,10 @@
 						<failOnError>true</failOnError>
 						<failOnWarnings>true</failOnWarnings>
 						<quiet>true</quiet>
+						<!-- Don't cross-link to sibling reactor modules: the native/bom
+						     modules have no Java sources, so link detection just creates
+						     fake apidocs dirs and logs "Error fetching link". -->
+						<detectOfflineLinks>false</detectOfflineLinks>
 					</configuration>
 				</plugin>
 				<plugin>