translate: essentials/template-refs

[tamnd]

Summary

Translate src/guide/essentials/template-refs.md to Vietnamese.

Scope: ref attribute, useTemplateRef(), function refs, refs on components

Translation conventions

• Sentence case headings
• Bilingual glossing: English term + Vietnamese in parentheses on first use
• English tech vocab preferred (property, function, component, ref, reactive)
• Code comments and template strings translated
• GLOSSARY.md terms applied consistently
• Full content parity with upstream English (vuejs/docs@6313f817)

Part 11 of 13 — Phase 3 (Essentials).