docs: add 'When to Activate' sections to 14 skill definitions

Add activation triggers to skills that were missing them, helping
Claude Code determine when to load each skill contextually.

skills/springboot-patterns/SKILL.md

@@ -7,6 +7,15 @@ description: Spring Boot architecture patterns, REST API design, layered service
 
 Spring Boot architecture and API patterns for scalable, production-grade services.
 
+## When to Activate
+
+- Building REST APIs with Spring MVC or WebFlux
+- Structuring controller → service → repository layers
+- Configuring Spring Data JPA, caching, or async processing
+- Adding validation, exception handling, or pagination
+- Setting up profiles for dev/staging/production environments
+- Implementing event-driven patterns with Spring Events or Kafka
+
 ## REST API Structure
 
 ```java