feat(maven): choose the JRE Maven runs with (#2020)

Closes #1976. Settings › Build Tools › Maven gets a JRE field (per project or global): empty uses the Project JDK, else the chosen JDK runs Maven sync, builds, goals and tests (JAVA_HOME). One resolver (ide_sdk::apply::maven_jdk / maven_build_env) now serves the build model, compile steps, Maven run configurations and the mvnd Java 17 check; an explicit JAVA_HOME in a run configuration still wins.

src/features/settings/languages/LanguagePages.tsx

@@ -498,6 +498,16 @@ export function MavenPage() {
   return (
     <div className={styles.page}>
       <Section>
+        <SdkRow
+          k="languages.java.maven.runnerJre"
+          label="JRE"
+          kind="jdk"
+          emptyLabel="Use Project JDK"
+          directory
+          browseTitle="Select JDK Home Directory"
+          aria-label="JRE"
+          hint="JDK used for Maven sync, builds, goals and tests. An explicit JAVA_HOME in a run configuration takes precedence."
+        />
         <SdkRow
           k="languages.java.maven.home"
           label="Maven home path"