fix: UI redesign — horizontal instance rows, proper scaling, readable tag cards

- Backend: add replicas field to InstanceResponse (extracted from values.replicaCount)
- InstanceCard: complete redesign as horizontal row layout
  - Status bar | Name+Chart | Replicas +/- | Action buttons
  - Scale controls show for deployed AND failed statuses (scale to 0)
  - Fix replicas display using new instance.replicas backend field
- InstancesManagementPage: vertical row list + onScale callback to update state
- TagCard: restore proper padding (p-4), min-width, readable button sizes
- ArtifactBrowserPage: reduce grid density (sm:1 md:2 lg:3)
- ModifyModal: simplify to YAML-only editing with current values pre-populated
  - Remove schema-based form generator
  - Keep values-diff as collapsible reference panel

frontend/src/features/artifact/registries/pages/ArtifactBrowserPage.tsx

@@ -525,7 +525,7 @@ const ArtifactBrowserPage: React.FC = () => {
                     description={`No tags matching "${tagSearchTerm}" found.`}
                   />
                 ) : (
-                  <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 xl:grid-cols-4 gap-3">
+                  <div className="grid grid-cols-1 sm:grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-4">
                     {filteredArtifacts.map((artifact, index) => (
                       <TagCard
                         key={`${artifact.repositoryName || "repo"}-${artifact.tag || index}`}