Desktop marketplace redesign: two-pane explorer with full catalog metadata (#13653)

* feat(desktop): add marketplace design exploration prototypes (storefront, explorer, registry)

Co-authored-by: Saoud Rizwan <saoudrizwan@users.noreply.github.com>

* fix(desktop): render catalog icon tiles without percentage padding

Co-authored-by: Saoud Rizwan <saoudrizwan@users.noreply.github.com>

* feat(desktop): drop placeholder icon tiles from explorer marketplace direction

Co-authored-by: Saoud Rizwan <saoudrizwan@users.noreply.github.com>

* feat(desktop): make explorer the marketplace view, drop design exploration harness

Co-authored-by: Saoud Rizwan <saoudrizwan@users.noreply.github.com>

* feat(desktop): add category tag filters to marketplace explorer

Co-authored-by: Saoud Rizwan <saoudrizwan@users.noreply.github.com>

* feat(desktop): collapse marketplace category pills behind a more toggle

* feat(desktop): remove maturity badges and CLI install section from marketplace

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Co-authored-by: Saoud Rizwan <saoudrizwan@users.noreply.github.com>
Co-authored-by: Cursor Agent <cursoragent@cursor.com>