Add AST-based code analysis with ast-grep

[burner-agent]

Summary

Integrate ast-grep/ast-grep (13k+ stars) for AST-based code search and refactoring during self-edit operations.

Motivation

When Burner's self-edit system (src/selfedit.ts) modifies its own source code, it relies on string-based operations. AST-based analysis would let the agent understand code structure, validate transformations are syntactically correct, and find specific patterns reliably — reducing the risk of self-edit breakage.

Proposal

• Install ast-grep CLI tool (Rust binary, fast)
• Use it in self-edit workflows to: validate edits produce valid syntax, search for code patterns structurally, perform safe automated refactors
• Could also be exposed as a skill so RALPH loops can use structural code search on any workspace

References

• https://github.com/ast-grep/ast-grep
• https://ast-grep.github.io