feat(weixin): add sticker draft command

[fawetian]

Description

Adds opencli weixin create-sticker for creating WeChat Official Account sticker drafts from a local image, optional title, and optional description. Updates the generated manifest, Weixin adapter docs, README command discovery, and adapter tests.

Related issue: N/A

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 🌐 New site adapter
• 📝 Documentation
• ♻️ 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/updated doc page under docs/adapters/
• Updated docs/adapters/index.md table
• Updated sidebar in docs/.vitepress/config.mts (not a 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

Checks run:

node --check clis/weixin/create-sticker.js
npx vitest run --project adapter clis/weixin/drafts.test.js
npm run build
npm run docs:build
git diff --check

Live smoke output from a logged-in Weixin session:

- status: sticker draft saved
  detail: '"塔勒布箴言" (sticker)'