Fix: Add missing syntax and normalize Auth Token usage

[Seol-JY]

📝 Key Changes

Fixes three syntax issues:

• Adds missing period in email validation message - c4bda53
• Adds missing 'from' keyword in import statement - db0a870
• Changes requiring discussion:
  • 이름 겹치지 않게 관리하기
  • For consistency between Code Example and Work on Improving sections, I added Auth Token to Code Example. Based on the document context, I believe adding Auth Token was appropriate - could you confirm if this assessment is correct? - 69a4ab2

🖼️ Before and After Comparison

Simple text corrections in documentation files. No visual changes.

[vercel]

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