docs(client-adoption): fix heading style for Quick Start section

Author: bsayli

docs/adoption/client-side-adoption.md

@@ -144,7 +144,7 @@ This shields your business code from generated artifacts and provides a stable c
 
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-7) Spring Boot Configuration — Quick Start (for demos/dev)
+## 7) Spring Boot Configuration — Quick Start (for demos/dev)
 
 For quick experiments or local development, you can wire the generated client with a simple RestClient: