refactor(subagent): split extension into modules

src/constants.ts

@@ -0,0 +1,10 @@
+import * as path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const SRC_DIR = path.dirname(fileURLToPath(import.meta.url));
+
+export const EXTENSION_DIR = path.dirname(SRC_DIR);
+export const EXTENSION_ENTRY = path.join(EXTENSION_DIR, "index.ts");
+export const PROMPTS_DIR = path.join(EXTENSION_DIR, "prompts");
+export const FINALIZE_TOOL_NAME = "subagent_finalize";
+export const MAX_FINALIZE_RETRIES = 2;