docs(browser): publish standalone package browser (#265)

Createa repository browser into Sphinx-managed static assets so Read the Docs.
Add a dedicated docs page, link it from the manual, and keep the release
tables as the primary download reference.

Assisted-by: Copilot:gpt-5.4-mini

Author: gsanchietti

README.rst

@@ -132,6 +132,10 @@ Finally, build the doc: ::
 
    make html
 
+The standalone package browser is published from ``_extra/browser/`` through
+``html_extra_path``. It is plain HTML, CSS, and JavaScript, so local and Read
+the Docs builds do not require a separate frontend toolchain.
+
 Localization workflow
 ---------------------