feat: add `fetch_task_file` function to retrieve task files from API

helpers.py

@@ -0,0 +1,18 @@
+import requests
+
+
+def fetch_task_file(api_url: str, task_id: str) -> tuple[bytes, str]:
+    """
+    Returns (file_bytes, content_type) or (b'', '') if no attachment found.
+    Follows any redirect the endpoint issues.
+    """
+    url = f"{api_url}/files/{task_id}"
+    try:
+        r = requests.get(url, timeout=15, allow_redirects=True)
+    except requests.RequestException as e:
+        print(f"[DEBUG] GET {url} failed → {e}")
+        return b"", ""
+    if r.status_code != 200:
+        print(f"[DEBUG] GET {url} → {r.status_code}")
+        return b"", ""
+    return r.content, r.headers.get("content-type", "").lower()