Refactor translator packages for OpenAI Chat Completions

- Renamed `openai` packages to `chat_completions` across translator modules.
- Introduced `openai_responses_handlers` with handlers for `/v1/models` and OpenAI-compatible chat completions endpoints.
- Updated constants and registry identifiers for OpenAI response type.
- Simplified request/response conversions and added detailed retry/error handling.
- Added `golang.org/x/crypto` for additional cryptographic functions.

internal/translator/gemini-cli/openai/responses/cli_openai-responses_request.go

@@ -0,0 +1,19 @@
+package responses
+
+import (
+	. "github.com/luispater/CLIProxyAPI/internal/translator/gemini/openai/responses"
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+)
+
+func ConvertOpenAIResponsesRequestToGeminiCLI(modelName string, rawJSON []byte, stream bool) []byte {
+	modelResult := gjson.GetBytes(rawJSON, "model")
+	rawJSON = []byte(gjson.GetBytes(rawJSON, "request").Raw)
+	rawJSON, _ = sjson.SetBytes(rawJSON, "model", modelResult.String())
+	if gjson.GetBytes(rawJSON, "systemInstruction").Exists() {
+		rawJSON, _ = sjson.SetRawBytes(rawJSON, "system_instruction", []byte(gjson.GetBytes(rawJSON, "systemInstruction").Raw))
+		rawJSON, _ = sjson.DeleteBytes(rawJSON, "systemInstruction")
+	}
+
+	return ConvertOpenAIResponsesRequestToGemini(modelName, rawJSON, stream)
+}

internal/translator/gemini-cli/openai/responses/gemini_openai-responses_request.go

@@ -1,5 +0,0 @@
-package responses
-
-func ConvertOpenAIResponsesRequestToGeminiCLI(modelName string, rawJSON []byte, stream bool) []byte {
-	return nil
-}