refactor(ripgrep): split into modular directory structure

[vtemian]

Summary

• Split monolithic ripgrep.ts (400+ lines) into modular directory structure
• Add Global.Platform helpers for cross-platform binary handling
• Add integration tests for ripgrep functionality

Changes

• src/file/ripgrep.ts → src/file/ripgrep/
  • index.ts - Public API (files, tree, search, rg)
  • binary.ts - Binary download/extraction logic
  • tree.ts - Tree building and BFS truncation
  • io.ts - Stream line parsing utility
• src/global/index.ts - Added Platform.isWindows and Platform.binExt
• test/file/ripgrep.test.ts - 14 integration tests