connectors: merge the catalog page into a row-list Connectors page

The standalone Catalog page added nothing the Connectors page could not
do: drop it (component, route, sidebar entry) and move its affordances
onto the Connectors page — the Add-connector dropdown (marketplace /
manual form, now at #connectors/new) and per-row removal for the admin.

Replace the card grid with a sharper row list (4px radius) built for
scanning status and acting; the marketplace's back link now returns to
#connectors. i18n keys renamed catalog.* -> connectors.add/new/*.

web/index.html

@@ -101,7 +101,6 @@
       <plugin-catalog-page></plugin-catalog-page>
       <plugin-detail-page></plugin-detail-page>
       <marketplace-page></marketplace-page>
-      <catalog-page></catalog-page>
       <profile-page style="display:none"></profile-page>
       <llm-providers-page></llm-providers-page>
       <models-hub-page></models-hub-page>