feat(i18n): src/content/learn/synchronizing-with-effects.md from English to Vietnamese

[KotonoSora]

🇻🇳 Vietnamese Translation: Synchronizing with Effects

Hi! I'm contributing as a volunteer translator for vi.react.dev, and this PR adds the Vietnamese translation for the "Synchronizing with Effects" lesson.

What's included

• Vietnamese translation of synchronizing-with-effects.md
• Preserved all code examples and markdown formatting
• Kept terminology consistent with existing translations

Changes

• ✅ Fully translated the guide covering React Effects, external system synchronization, and Effect lifecycle management
• ✅ Maintained code blocks, links, Sandpack components and Challenge/Solution sections
• ✅ Verified all internal links and formatting render correctly

Looking forward to contributing more translations to the project! 🚀

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Tóm tắt những gì đã được dịch:

Tiêu đề và phần Intro:
"Synchronizing with Effects" → "Đồng bộ hóa với Effect"

Các phần chính:

• "What are Effects and how are they different from events?" → "Effect là gì và chúng khác với event như thế nào?"
• "You might not need an Effect" → "Bạn có thể không cần Effect"
• "How to write an Effect" → "Cách viết một Effect"
• "How to handle the Effect firing twice in development?" → "Cách xử lý Effect kích hoạt hai lần trong quá trình phát triển?"
• "Putting it all together" → "Kết hợp tất cả lại"

Phần Challenges:

• "Focus a field on mount" → "Focus một trường khi mount"
• "Focus a field conditionally" → "Focus một trường có điều kiện"
• "Fix an interval that fires twice" → "Fix an interval that fires twice"
• "Fix fetching inside an Effect" → "Fix fetching inside an Effect"

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1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
vi-legacy-reactjs-org	⬜️ Ignored (Inspect)	Visit Preview		Jun 16, 2025 3:59am

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