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/shared/__tests__/support-prompts.test.ts

@@ -77,12 +77,11 @@ describe("Code Action Prompts", () => {
 	describe("ENHANCE action", () => {
 		it("should format enhance prompt correctly", () => {
 			const prompt = supportPrompt.create("ENHANCE", {
-				filePath: testFilePath,
-				selectedText: testCode,
+				userInput: "test",
 			})
 
 			expect(prompt).toBe(
-				"Generate an enhanced version of this prompt (reply with only the enhanced prompt - no conversation, explanations, lead-in, bullet points, placeholders, or surrounding quotes):",
+				"Generate an enhanced version of this prompt (reply with only the enhanced prompt - no conversation, explanations, lead-in, bullet points, placeholders, or surrounding quotes):\n\ntest",
 			)
 			// Verify it ignores parameters since ENHANCE template doesn't use any
 			expect(prompt).not.toContain(testFilePath)