Add ast-grep provider for AST-aware code search and transformation

[amondnet]

Summary

Add ast-grep tools and skill to dora MCP server for AST-aware code search and transformation capabilities.

AST-aware search understands code structure (unlike text-based grep), enabling queries like "find async functions without error handling".

Context

• Reference implementation: ref/oh-my-opencode/src/tools/ast-grep/
• Architecture decision: docs/adr/0001-ast-grep-integration-architecture.md

Features to Implement

MCP Tools

• ast_grep_search - AST-aware code search
• ast_grep_replace - AST-aware code transformation

Language Support

• CLI: 25+ languages supported
• NAPI bindings: 5 languages (faster in-memory transforms)
• Binary auto-download from GitHub releases
• YAML rule file support

Agent/Skill

• Rule writing guidance and examples

Architecture

packages/dora/src/providers/ast-grep/
├── index.ts        # AstGrepProvider
├── cli.ts          # CLI wrapper
├── downloader.ts   # Binary download
├── napi.ts         # NAPI bindings
├── constants.ts    # Config
├── types.ts        # Types
└── utils.ts        # Formatting

agents/ast-grep.md  # Rule writing skill

Tasks

• T001 [P] Create types.ts with interfaces (CliMatch, SgResult, etc.)
• T002 [P] Create constants.ts with languages, platform config, defaults
• T003 Create downloader.ts for binary auto-download (depends on T002)
• T004 Create cli.ts with runSg function (depends on T002, T003)
• T005 [P] Create napi.ts for in-memory transforms
• T006 [P] Create utils.ts for result formatting
• T007 Create index.ts AstGrepProvider (depends on T001-T006)
• T008 Export provider from packages/dora/src/providers/index.ts (depends on T007)
• T009 Register provider in packages/dora/src/server.ts (depends on T008)
• T010 Create agents/ast-grep.md skill for rule writing
• T011 Add unit tests for ast-grep provider
• T012 Add integration tests for ast-grep tools

Acceptance Criteria

• All tasks completed and tested
• ast-grep provider fully functional and integrated into dora MCP server
• Documentation updated with ast-grep tool usage
• Agent skill provides helpful guidance for rule writing