Add Zhipu and Z.ai providers

[Manho]

Summary

• add Zhipu (China) and Z.ai (Global) as optional providers
• use the official Zhipu/Z.ai logo and update provider naming
• support image attachment injection for both providers
• raise the panel limit to 12 and add 1x12 and full 2x6 layouts
• update settings, localization, documentation, and automated coverage

Root cause

The Zhipu China attachment integration initially targeted the inactive .img-input element. The current site routes local uploads through Element Plus' .el-upload__input, so attachments never reached the active composer. The integration now targets the active upload input, mounts it through the attachment control when needed, and confirms success by waiting for the real preview list.

Validation

• npx vitest run --silent=true --exclude 'tests/e2e/**' — 302 tests passed
• npx playwright test tests/e2e/*.e2e.test.js — 32 tests passed
• npm run release:package — passed
• real-browser verification confirmed attachment previews in both Zhipu (China) and Z.ai (Global)
• real-browser verification confirmed the 1x12 and 2x6 layout options