refactor: generalize prompt enhancement into single completion handler

- Rename enhance-prompt.ts to single-completion-handler.ts for better clarity
- Refactor enhancement logic to be more generic and reusable
- Update prompt template handling to use template literals
- Adjust tests and imports accordingly

src/utils/single-completion-handler.ts

@@ -0,0 +1,24 @@
+import { ApiConfiguration } from "../shared/api"
+import { buildApiHandler, SingleCompletionHandler } from "../api"
+
+/**
+ * Enhances a prompt using the configured API without creating a full Cline instance or task history.
+ * This is a lightweight alternative that only uses the API's completion functionality.
+ */
+export async function singleCompletionHandler(apiConfiguration: ApiConfiguration, promptText: string): Promise<string> {
+	if (!promptText) {
+		throw new Error("No prompt text provided")
+	}
+	if (!apiConfiguration || !apiConfiguration.apiProvider) {
+		throw new Error("No valid API configuration provided")
+	}
+
+	const handler = buildApiHandler(apiConfiguration)
+
+	// Check if handler supports single completions
+	if (!("completePrompt" in handler)) {
+		throw new Error("The selected API provider does not support prompt enhancement")
+	}
+
+	return (handler as SingleCompletionHandler).completePrompt(promptText)
+}