feat: add --download_only flag and visdom-download CLI for offline setups

Adds a dedicated mechanism to download all required static assets
(JS, CSS, fonts) without starting the Tornado server. This addresses
the workflow described in issue #942 where users on air-gapped machines
need to pre-download assets on an online machine.

Three ways to use:
  - visdom --download_only
  - visdom-download
  - python -m visdom.server --download_only

Closes #942

Author: pankajbaid567

py/visdom/server/run_server.py

@@ -69,7 +69,7 @@ def start_server(
     app.sources = []
 
 
-def main(print_func=None):
+def main(print_func=None, _download_only=False):
     """
     Run a server from the command line, first parsing arguments from the
     command line
@@ -143,8 +143,21 @@ def main(print_func=None):
         action="store_true",
         help="Load data from filesystem when starting server (and not lazily upon first request).",
     )
+    parser.add_argument(
+        "--download_only",
+        default=False,
+        action="store_true",
+        help="Download all required scripts (JS, CSS, fonts) and exit "
+        "without starting the server. Useful for offline/air-gapped setups.",
+    )
     FLAGS = parser.parse_args()
 
+    download_scripts()
+
+    if FLAGS.download_only or _download_only:
+        print("Downloaded all required scripts. Exiting.")
+        return
+
     # Process base_url
     base_url = FLAGS.base_url if FLAGS.base_url != DEFAULT_BASE_URL else ""
     assert base_url == "" or base_url.startswith("/"), "base_url should start with /"
@@ -232,9 +245,13 @@ def main(print_func=None):
 
 
 def download_scripts_and_run():
-    download_scripts()
     main()
 
 
+def download_only():
+    """Download all required scripts and exit without starting the server."""
+    main(_download_only=True)
+
+
 if __name__ == "__main__":
     download_scripts_and_run()

setup.py

@@ -70,5 +70,8 @@ def get_dist(pkgname):
     include_package_data=True,
     zip_safe=False,
     install_requires=requirements,
-    entry_points={'console_scripts': ['visdom=visdom.server.run_server:download_scripts_and_run']}
+    entry_points={'console_scripts': [
+        'visdom=visdom.server.run_server:download_scripts_and_run',
+        'visdom-download=visdom.server.run_server:download_only',
+    ]}
 )