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>

deploy/base/server.yaml

@@ -36,6 +36,16 @@ spec:
                 secretKeyRef:
                   name: postgres-credentials
                   key: POSTGRES_PASSWORD
+            - name: SPRING_FLYWAY_USER
+              valueFrom:
+                secretKeyRef:
+                  name: postgres-credentials
+                  key: POSTGRES_USER
+            - name: SPRING_FLYWAY_PASSWORD
+              valueFrom:
+                secretKeyRef:
+                  name: postgres-credentials
+                  key: POSTGRES_PASSWORD
             - name: OPENSEARCH_URL
               value: "http://opensearch.cameleer.svc.cluster.local:9200"
             - name: CAMELEER_OPENSEARCH_INDEX_PREFIX