docs: Remove build command from agent instructions (#5873)

Drop the "Build entire project" command from AGENTS.md Essential
Commands so agents aren't instructed to run a full ./gradlew build,
which is an expensive step not needed for the documented workflow.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: runningcode

AGENTS.md

@@ -34,9 +34,6 @@ The project uses **Gradle** with Kotlin DSL. Key build files:
 # Run all tests and linter
 ./gradlew check
 
-# Build entire project
-./gradlew build
-
 # Generate documentation
 ./gradlew aggregateJavadocs
 ```