docs: correct MySQL skill repository registration

[mvanhorn]

AgentScope-Java Version

Documentation-only change against the docs/v2 tree; it corrects a code
sample and is not tied to one dependency version. The corrected snippet uses
ReActAgent.Builder.skillRepository(...), which is the current v2 API.

Description

Replace the invalid Toolkit registration block in both localized quickstarts with the established ReActAgent.builder() flow, passing the existing MysqlSkillRepository instance to skillRepository(...). Add the imports and minimal agent builder context needed for each snippet to communicate where the repository belongs, following the examples in the building-block documentation. Keep repository construction, database setup, schema, and CRUD guidance unchanged because those sections describe valid APIs and are outside the reported defect.

The Chinese MySQL skill repository quickstart instructs users to pass loaded skills to Toolkit.registerSkill, but Toolkit has no such method. The English counterpart contains the same invalid call, so users following either version receive a compile-time error. In the current API, repositories are attached to an agent through ReActAgent.Builder.skillRepository(...), which installs the dynamic skill middleware during agent construction. The defect is confined to the paired documentation examples; the repository and agent APIs already support the intended integration.

Fixes #2657

Checklist

Please check the following items before code is ready to be reviewed.

• Code has been formatted with mvn spotless:apply
  Not run: no test command resolved in this workspace, so nothing was executed to pass.
• All tests are passing (mvn test)
  Not run: no test command resolved in this workspace, so nothing was executed to pass.
• Javadoc comments are complete and follow project conventions
  N/A: this PR changes Markdown documentation only, no Java sources.
• Related documentation has been updated (e.g. links, examples, etc.)
  This PR is the documentation update: both the English and Chinese
  MySQL skill-repository quickstarts.
• Code is ready for review

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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