i18n(zh-CN): add missing Secure Encalve & User Key pages and unify te…

[Vstory]

Summary

Add missing Simplified Chinese (zh-CN) translations and align terminology across the docs: 2 new concept pages (Secure Encalve / User Key), 2 missing sections in 1.Why MajorPrivacy.md, plus a terminology and proofreading pass over the existing zh-CN corpus.

What was done

• Added two missing concept pages (translated from upstream EN):
  • zh-CN/1.Basic Introduction/Related Conception/Secure Encalve.md
  • zh-CN/1.Basic Introduction/Related Conception/User Key.md
• Filled two missing sections in zh-CN/1.Basic Introduction/1.Why MajorPrivacy.md (Secure Volume / Tweak Engine).
• Terminology pass: unified Secure Volume to 加密卷 across the zh-CN corpus, following the Windows Simplified Chinese ecosystem (matches VeraCrypt's official zh-CN term).
• Removed EN/zh bilingual duplication in concept page titles; keep pure Chinese titles.
• Proofreading pass: fixed typos, missing spacing, and heading consistency across zh-CN files.

Terminology

• Secure Volume -> 加密卷 (official Windows zh-CN ecosystem term; not 受保护卷)
• UI/panel and concept terms translated into Chinese where possible: Secure Enclave -> 安全飞地, Tweak Engine -> 微调引擎, User Key -> 用户密钥
• Product brand MajorPrivacy kept in English; a few concept pages keep the English term with a Chinese gloss (e.g. Enclave（隔离区）) for clarity
• Upstream file name Secure Encalve.md kept as-is (known upstream typo) to stay in sync with the EN tree

Verification

• Changes are zh-CN only; English source and other languages are untouched
• The 0-byte placeholder Resource Protection.md (upstream EN page still empty) is intentionally not included
• Single commit on current upstream main — no conflicts