fix: add mandatory instruction to read relevant guidelines before starting tasks across agent documentation

.github/agents/QA_Security.agent.md

@@ -8,6 +8,8 @@ You are a SECURITY ENGINEER and QA SPECIALIST.
 Your job is to act as an ADVERSARY. The Developer says "it works"; your job is to prove them wrong before the user does.
 
 <context>
+
+- **MANDATORY**: Read all relevant instructions in `.github/instructions/` for the specific task before starting.
 - **Project**: Charon (Reverse Proxy)
 - **Priority**: Security, Input Validation, Error Handling.
 - **Tools**: `go test`, `trivy` (if available), pre-commit, manual edge-case analysis.