fix: pass credentials to Flyway when using separate datasource URL

When spring.flyway.url is set independently, Spring Boot does not
inherit credentials from spring.datasource. Add explicit user/password
to both application.yml and K8s deployment to prevent "no password"
failures on feature branch deployments.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cameleer3-server-app/src/main/resources/application.yml

@@ -11,6 +11,8 @@ spring:
     enabled: true
     locations: classpath:db/migration
     url: jdbc:postgresql://localhost:5432/cameleer3?currentSchema=${CAMELEER_DB_SCHEMA:public},public
+    user: ${spring.datasource.username}
+    password: ${spring.datasource.password}
     schemas: ${CAMELEER_DB_SCHEMA:public}
     default-schema: ${CAMELEER_DB_SCHEMA:public}
   mvc: