feat: add emphasis expressions to key configuration rules (#35)

Add IMPORTANT, CRITICAL, and YOU MUST expressions to improve
instruction following reliability per Anthropic best practices:
- global/CLAUDE.md: IMPORTANT in Priority Rules section
- project/CLAUDE.md: CRITICAL in Quick Reference section
- conversation-language.md: YOU MUST for Korean response rule
- security.md: IMPORTANT for input validation section

Closes #29

Author: kcenon

global/CLAUDE.md

@@ -15,6 +15,8 @@ The configuration is organized into focused modules for better token efficiency:
 
 ## Priority Rules
 
+**IMPORTANT:** These rules determine which settings take effect:
+
 1. **Project settings override global settings** - When a project has its own `CLAUDE.md`, those rules take precedence
 2. **Intelligent loading** - Claude Code uses conditional loading rules to automatically select relevant modules (see project's `conditional-loading.md`)
 3. **Explicit conflicts** - If project and global settings conflict, the project setting wins

global/conversation-language.md

@@ -11,6 +11,7 @@ Claude communicates with users in their preferred language while maintaining tec
 
 ### User Interaction
 - **Default response language**: Korean
+  - **YOU MUST:** Always respond in Korean unless the user explicitly requests English.
 - **Language switching**: Honor explicit user requests to change language
 - **Consistency**: Maintain chosen language throughout session
 

project/CLAUDE.md

@@ -9,6 +9,8 @@ These guidelines define general conventions and practices for working in this re
 
 ## Quick Reference
 
+**CRITICAL:** Always consult [environment.md](claude-guidelines/environment.md) first for timezone and locale context.
+
 <table>
 <tr>
 <td width="50%">

project/claude-guidelines/security.md

@@ -2,6 +2,8 @@
 
 ## Input Validation
 
+**IMPORTANT:** All user input MUST be validated before processing.
+
 ### Validate All External Input
 
 Never trust data from external sources. Always validate and sanitize: