docs: move license to footer and update to AGPL v3.0 or later

[hzhangxyz]

No description provided.

[Copilot]

Pull request overview

This PR reorganizes license information by moving it from the documentation index pages to a centralized footer configuration, while simultaneously updating the license type from GPL v3.0 to AGPL v3.0.

• Removes license sections from both English and Chinese documentation index pages
• Updates README.md license reference from GPL to AGPL v3.0
• Adds footer configuration in VitePress with license and copyright information for both language versions

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
docs/zh/index.md	Removes the Chinese license section (4 lines) that was previously at the bottom of the documentation index
docs/en/index.md	Removes the English license section (4 lines) that was previously at the bottom of the documentation index
README.md	Updates license text from "GNU General Public License" to "GNU Affero General Public License"
.vitepress/config.mts	Adds footer configuration with license message and copyright for both English and Chinese locales

The changes are clean and consistent. The license information has been successfully centralized in the VitePress footer configuration while maintaining consistency across both language versions. The license update from GPL to AGPL is properly reflected in all relevant locations.

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