test: disable ActivityImageService manual test class in default build

The test method was already disabled, but the Spring test context for the class was still being created during the regular test run. Moving `@Disabled` to the class prevents the Testcontainers-based application context from loading for this manual-only test and stops `verify` from failing.

Signed-off-by: Marcus Fihlon <marcus@fihlon.swiss>

src/test/java/net/javahippie/fitpub/service/ActivityImageServiceTest.java

@@ -27,12 +27,16 @@ import static org.junit.jupiter.api.Assertions.*;
 /**
  * Manual test for ActivityImageService.
  * These tests are disabled by default and should only be run manually.
+ *
+ * To run this test manually:
+ * mvn test -Dtest=ActivityImageServiceTest
  */
 @SpringBootTest(properties = {
         "fitpub.image.osm-tiles.enabled=true"
 })
 @ActiveProfiles("test")
 @Import(TestcontainersConfiguration.class)
+@Disabled("Manual test - run explicitly when needed")
 class ActivityImageServiceTest {
 
     @Autowired
@@ -55,7 +59,6 @@ class ActivityImageServiceTest {
      * mvn test -Dtest=ActivityImageServiceTest#testGenerateActivityImage_Manual
      */
     @Test
-    @Disabled("Manual test - run explicitly when needed")
     @DisplayName("Generate activity image from test FIT file")
     void testGenerateActivityImage_Manual() throws Exception {
         // Load test FIT file