Fixes#40683
`PluginInstaller.list_plugins_by_category` calls
`GET /plugin/{tenant_id}/management/{category}/list` on the plugin
daemon. Local plugin daemons (e.g. 0.6.x) don't expose the
category-segmented route and return 404. The current code raises
this 404, which then breaks the model-provider integration page
even though the generic listing route is available.
On 404, fall back to
`GET /plugin/{tenant_id}/management/list` and filter the result
locally by `declaration.category`. The generic route is the same
one used by the unrestricted `list_plugins_with_total`. Apply the
caller's page/page_size on the filtered result (cap page_size at
1000 for the fallback fetch — adequate for any reasonable category).
Added a regression test in `test_plugin_manager.py` that
asserts the 404-fallback path produces the correct filtered list
with the right `has_more` flag.
dcdca603e7