feat(zhihu): add interaction commands

[Astro-Han]

Description

Add core Zhihu interaction commands for logged-in browser sessions:

• zhihu follow
• zhihu like
• zhihu favorite
• zhihu comment
• zhihu answer

Also adds typed target parsing, shared write-safety helpers, adapter tests, and Zhihu adapter docs updates.

Related issue: #857

Type of Change

• ✨ New feature
• 🌐 New site adapter
• 📝 Documentation
• 🐛 Bug fix
• ♻️ Refactor
• 🔧 CI / build / tooling

Checklist

• I ran the checks relevant to this PR
• I updated tests or docs if needed
• I included output or screenshots when useful

Documentation (if adding/modifying an adapter)

• Added doc page under docs/adapters/ (if new adapter)
• Updated docs/adapters/index.md table (if new adapter)
• Updated sidebar in docs/.vitepress/config.mts (if new adapter)
• Updated README.md / README.zh-CN.md when command discoverability changed
• Used positional args for the command's primary subject unless a named flag is clearly better
• Normalized expected adapter failures to CliError subclasses instead of raw Error

Screenshots / Output

Verified locally:

• pnpm typecheck
• pnpm test
• pnpm test:adapter
• pnpm docs:build
• npx vitest run tests/e2e/browser-public.test.ts -t "zhihu hot returns trending questions|zhihu search returns results"

Known limitation during verification:

• pnpm test:e2e is not fully green in this environment because two existing external-site tests are flaky / environment-sensitive:
  • tieba read limit counts replies instead of consuming the main post slot
  • imdb top returns chart data
• These failures are not introduced by this branch. The same targeted tests pass when rerun individually on both main and this branch.