fix: attach OTEL javaagent directly in bootRunWithObservability

The previous approach set OTEL_JAVAAGENT_ENABLED via `environment` in a
doFirst block, but bootRun's System.getenv() check runs at Gradle
configuration time (before any task executes), so the javaagent flag was
never added. Fix by adding jvmArgs directly in the doFirst block.

Also clarify copyOtelAgent comment: it's a standalone helper for IntelliJ
run configurations, not used by bootRun or bootRunWithObservability.

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

Author: Anty0

backend/app/build.gradle

@@ -298,7 +298,10 @@ bootRun {
     }
 }
 
-// Copy OTEL agent to a predictable location for IntelliJ usage
+// Copy OTEL agent JAR to a predictable location for manual IntelliJ run configuration.
+// Not used by bootRun or bootRunWithObservability (they resolve the agent from Gradle's dependency cache).
+// Usage: ./gradlew server-app:copyOtelAgent → build/otel/opentelemetry-javaagent.jar
+// Then add -javaagent:backend/app/build/otel/opentelemetry-javaagent.jar to your IntelliJ VM options.
 // See: docs/observability/
 tasks.register('copyOtelAgent', Copy) {
     from configurations.otelAgent
@@ -317,6 +320,12 @@ tasks.register('bootRunWithObservability') {
             // Spring profile
             args '--spring.profiles.active=dev'
 
+            // Attach the OTEL javaagent directly. We cannot rely on bootRun's
+            // System.getenv("OTEL_JAVAAGENT_ENABLED") check because that runs at Gradle
+            // configuration time (before any task executes), while this doFirst block
+            // runs at execution time.
+            jvmArgs "-javaagent:${configurations.otelAgent.singleFile.absolutePath}"
+
             // OTEL configuration
             environment 'OTEL_JAVAAGENT_ENABLED', 'true'
             environment 'OTEL_SERVICE_NAME', 'tolgee-platform'