fix(ci): set management.server.port=0 in test profile to fix 25-min test timeout

Port 8081 was fixed by #576. With four @DirtiesContext(AFTER_EACH_TEST_METHOD)
classes (22 context restarts total), the OS TIME_WAIT state holds port 8081
for ~45-60s per cycle — adding ~17 min overhead. All 1601 tests pass but
surefire's 10-min timeout fires before the suite finishes.

Fixes #593.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/test/resources/application-test.yaml

@@ -23,6 +23,8 @@ otel:
 # Disable trace export in tests — prevents OTLP connection attempts when no Tempo is running.
 # Sampling probability 0.0 means no spans are created, so no export is attempted.
 management:
+  server:
+    port: 0   # random port per context — prevents TIME_WAIT conflicts when @DirtiesContext restarts the context
   tracing:
     sampling:
       probability: 0.0