feat(translator): add built-in translator registry and helpers

- Introduced `builtin` package exposing a default registry and pipeline for built-in translators.
- Added format constants for common schemas (e.g., OpenAI, Gemini, Codex).
- Implemented helper functions for schema translation using format name strings.
- Provided example usage for integration with translator helpers.

sdk/translator/formats.go

@@ -0,0 +1,11 @@
+package translator
+
+// Common format identifiers exposed for SDK users.
+const (
+	FormatOpenAI         Format = "openai"
+	FormatOpenAIResponse Format = "openai-response"
+	FormatClaude         Format = "claude"
+	FormatGemini         Format = "gemini"
+	FormatGeminiCLI      Format = "gemini-cli"
+	FormatCodex          Format = "codex"
+)