config(app): silence MustacheAutoConfiguration templates-dir warning

jmustache on the classpath (for alert notification templates) triggers
Spring Boot's MustacheAutoConfiguration, which warns about the missing
classpath:/templates/ folder we don't use. Disable its check.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -18,6 +18,8 @@ spring:
   mvc:
     async:
       request-timeout: -1
+  mustache:
+    check-template-location: false
   jackson:
     serialization:
       write-dates-as-timestamps: false