fix(#152): disable open-in-view to prevent HikariPool exhaustion

spring.jpa.open-in-view=true (the default) holds a DB connection open for
the entire HTTP request lifecycle. Under concurrent dashboard API calls
(Promise.allSettled fires 3 at once), the pool of 10 is exhausted and the
backend crashes with connection timeout errors.

Setting open-in-view=false releases connections as soon as each
@Transactional method completes.

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

backend/src/main/resources/application.yaml

@@ -12,6 +12,7 @@ spring:
     enabled: false  # Managed explicitly via FlywayConfig bean
 
   jpa:
+    open-in-view: false  # Prevents holding DB connections for the full HTTP request lifecycle
     hibernate:
       ddl-auto: none
     properties: