chore(agents): add Korean response rule to AGENTS.md

AGENTS.md

@@ -13,6 +13,7 @@ Guardrails
 - Safety: avoid destructive actions (file deletions, rewrites, config changes) unless explicitly requested.
 - Responses: be concise; code first, short rationale after. If uncertain, prefix with "Uncertain:". If multiple viable solutions, show the top 2 briefly.
 - Planning: for multi‑step tasks, maintain an update_plan with exactly one in_progress step.
+- Language: 기본적으로 한국어로 응답합니다. (필요 시 코드/로그/명령어는 원문 유지)
 
 Coding Standards
 - Language: Dart/Flutter (SDK >= 3.0). Respect `analysis_options.yaml` (flutter_lints baseline).
@@ -66,4 +67,3 @@ References & External Facts
 Notes from ~/.claude (adapted)
 - Few‑shot examples improve accuracy; include small before/after or sample input→output when helpful.
 - Use structured thinking internally; present only concise, actionable outputs here.
-