feat: add .cts extension support to ctx.ast() TypeScript language

[rhuanbarreto]

Context

From PR #452 review: .cts is not in AST_LANGUAGE_EXTENSIONS.typescript, so ctx.ast("file.cts", "typescript") is rejected by the plausibility guardrail. This is conservative but may be needed as .cts files appear in the wild.

Proposal

1. Add ".cts" to AST_LANGUAGE_EXTENSIONS.typescript in src/engine/ast-support.ts
2. In the TypeScript branch of runner.ts, detect .cts and pass sourceType: "script" to parseJsModule (mirroring the .cjs handling)
3. Add a test in tests/engine/runner-ast.test.ts analogous to the existing .cjs/.mjs test

References

• PR feat: ast-aware rule context (ctx.ast) for TS/JS/Python/Ruby #452 review thread on .cts support
• Files: src/engine/ast-support.ts, src/engine/runner.ts, tests/engine/runner-ast.test.ts