build: add j3r452-only src/main/java-amdh source root

Empty for now; Epic 3 fills it with OnUpgradeListener bridge classes.

applet/pom.xml

@@ -164,6 +164,31 @@
                 <cap.elf.aid>A0000009094454414C49524F02</cap.elf.aid>
                 <cap.output.name>aliro-applet-j3r452.cap</cap.output.name>
             </properties>
+            <build>
+                <plugins>
+                    <!--
+                        AMD-H bridge classes (e.g. OnUpgradeListener implementations) live
+                        under src/main/java-amdh and are only compiled into the j3r452 CAP.
+                        Keeping them out of the j3r180 source set prevents org.globalplatform.upgrade
+                        imports from leaking into the J3R180 build, which lacks the AMD-H API.
+                    -->
+                    <plugin>
+                        <groupId>org.codehaus.mojo</groupId>
+                        <artifactId>build-helper-maven-plugin</artifactId>
+                        <version>3.6.0</version>
+                        <executions>
+                            <execution>
+                                <id>add-amdh-sources</id>
+                                <phase>generate-sources</phase>
+                                <goals><goal>add-source</goal></goals>
+                                <configuration>
+                                    <sources><source>src/main/java-amdh</source></sources>
+                                </configuration>
+                            </execution>
+                        </executions>
+                    </plugin>
+                </plugins>
+            </build>
         </profile>
     </profiles>
 </project>