DEVX-1: fix: add User-Agent header to _download in install_tools

src/devx/tools/install_tools.py

@@ -65,8 +65,13 @@ def _ensure_target_dir() -> Path:
 
 
 def _download(url: str, dest: Path) -> None:
-    """Download a file from ``url`` to ``dest`` with a 60s timeout."""
-    with urllib.request.urlopen(url, timeout=60) as resp, open(dest, "wb") as f:  # nosec B310
+    """Download a file from ``url`` to ``dest`` with a 60s timeout.
+
+    A User-Agent header is set because some CDNs (e.g. dl.gitea.com)
+    return 403 to requests with Python's default User-Agent.
+    """
+    req = urllib.request.Request(url, headers={"User-Agent": "devx/install-tools"})
+    with urllib.request.urlopen(req, timeout=60) as resp, open(dest, "wb") as f:  # nosec B310
         shutil.copyfileobj(resp, f)