Add ESLint rules to enforce import grouping and ordering

[coderabbitai]

Description

ESLint configuration should enforce proper import grouping to separate external dependencies from local imports and maintain consistent ordering.

Context

This issue was identified during code review where external dependencies (e.g., react-router, antd) were mixed with local imports (./router, ./theme) in the same import group, reducing code readability and maintainability.

Expected Behaviour

ESLint should enforce:

• Separation of external dependencies from local imports
• Consistent ordering within each group (alphabetical or logical)
• Clear grouping boundaries between different import types

Related Links

• Original PR: feat(new-webui): Add global theming config and adjust sider appearance. clp#937
• Code review comment: feat(new-webui): Add global theming config and adjust sider appearance. clp#937 (comment)

Requested by: @junhaoliao