fix(zhihu): decode numeric entities in text output

[lenovobenben]

Summary

• add a shared Zhihu text helper for HTML stripping and entity decoding
• decode decimal and hex numeric entities in search, question, and collection list output
• keep answer-detail and answer-comments paragraph-preserving behavior while reusing the shared helper

Why

Some Zhihu API fields include numeric HTML entities such as " and &. Search/question/collection output could expose those raw entities even though answer-detail already decoded them.

Validation

• npx vitest run --project adapter clis/zhihu/text.test.js clis/zhihu/search.test.js clis/zhihu/question.test.js clis/zhihu/collection.test.js clis/zhihu/answer-detail.test.js clis/zhihu/answer-comments.test.js
• npm run check:typed-error-lint
• npm run check:silent-column-drop
• git diff --check
• npm run dev -- zhihu search "Claude Code vs Codex?" --limit 5 -f json