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

backend/internal/adapter/input/http/dto/instance_dto.go

@@ -73,6 +73,7 @@ type InstanceResponse struct {
 	LastError      string                 `json:"lastError,omitempty"`
 	Revision       int                    `json:"revision"`
 	Values         map[string]interface{} `json:"values,omitempty"`
+	Replicas       int                    `json:"replicas"`
 	CreatedAt      string                 `json:"createdAt"`
 	UpdatedAt      string                 `json:"updatedAt"`
 }