build: target Java 8 instead of 7

JDK 20+ removed -source/-target 7, so the module no longer compiled on
modern JDKs. Bump source.level to 8 (lowest still supported).

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

pom.xml

@@ -47,7 +47,7 @@
   </prerequisites>
 
   <properties>
-    <source.level>1.7</source.level>
+    <source.level>8</source.level>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
   </properties>