feat(brainstorm): enforce Chinese language for all user questions

Add mandatory Chinese language rule for AskUserQuestion in artifacts.md and synthesis.md:
- Phase 3 Rules: Questions MUST be asked in Chinese (用中文提问)
- Question Generation Guidelines: ALL questions MUST be in Chinese (所有问题必须用中文)
- Phase 4 (synthesis.md): ALL AskUserQuestion calls MUST use Chinese

Rationale: Improve user understanding and interaction experience for Chinese-speaking users

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.claude/commands/workflow/brainstorm/artifacts.md

@@ -82,6 +82,7 @@ FOR each selected role:
 ```
 
 **Rules**:
+- ✅ Questions MUST be asked in Chinese (用中文提问) for better user understanding
 - ✅ Questions MUST reference Phase 1 keywords (e.g., "real-time", "100 users")
 - ✅ Options MUST be concrete approaches, explain relevance to topic
 - ❌ NEVER generic "Architecture style?" without task context
@@ -191,6 +192,7 @@ function generate(role, challenges) {
 ```
 
 **Quality Rules**:
+- ✅ ALL questions MUST be in Chinese (所有问题必须用中文)
 - ✅ Reference topic keywords in every question
 - ✅ Options are concrete technical choices (not abstract categories)
 - ✅ Descriptions explain relevance to topic