Improve Windows Python setup guidance

src/services/python-json-worker.ts

@@ -172,7 +172,21 @@ export class PythonJsonWorker {
     });
 
     child.on("error", (error) => {
-      this.rejectAll(error as Error);
+      const spawnError = error as NodeJS.ErrnoException;
+      if (spawnError.code === "ENOENT") {
+        this.rejectAll(
+          new Error(
+            [
+              `Python 실행에 실패했습니다: ${launch.command}`,
+              "Windows면 `.env` 에 `LOCAL_AI_PYTHON=py -3` 를 넣고 다시 실행하세요.",
+              "최초 1회는 `bun run setup:local-ai` 를 먼저 실행해야 합니다.",
+            ].join("\n"),
+          ),
+        );
+        return;
+      }
+
+      this.rejectAll(spawnError);
     });
 
     this.child = child;