fix(test): use ddl-auto=create to prevent cross-context table drops

Multiple @SpringBootTest classes with different @MockBean configs
cause separate Spring contexts sharing the same H2 in-memory database.
With create-drop, one context's shutdown drops tables needed by another,
causing "Table not found (this database is empty)" errors.

server/skillhub-app/src/test/resources/application-test.yml

@@ -10,7 +10,7 @@ spring:
     password:
   jpa:
     hibernate:
-      ddl-auto: create-drop
+      ddl-auto: create
     database-platform: org.hibernate.dialect.H2Dialect
   flyway:
     enabled: false