Add query observability to the Ktor integration

[zantvoort]

Storm already ships Ktor integration; the 1.13.0 milestone tightens it, in step with the Spring Boot work. This issue covers observability.

Same signal as the Spring side (#203), different binding: Ktor apps typically run the MicrometerMetrics plugin and/or the OpenTelemetry agent. Storm should emit query observations with the same tags (entity/projection, repository, operation) through the core observer hook (#198), and spans should nest correctly under Ktor's server spans.

Tasks:

• Bind the core query observer to Micrometer when it is on the classpath
• Verify span nesting with OpenTelemetry
• Docs