WIP：feat:add ast-grep to OpenViking

[Mijamind719]

Description

- add AST-based code search endpoint: POST /api/v1/search/ast-grep
- implement VikingFS ast_grep with sg command integration,
  file materialization, output parsing, and error handling
- expose ast_grep in FSService, local/async/sync clients,
  and HTTP client stack
- add Python CLI ast-grep command and Rust CLI ast-grep command support
- update English/Chinese API and architecture docs for ast-grep usage/examples
- add tests for server API, SDK client, Python client,
  and CLI help for ast-grep

Related Issue

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Additional Notes

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