chore: Remove dss-claude-plugin directory

Removing obsolete plugin directory after consolidation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

dss-claude-plugin/core/skins/workbench.json

@@ -1,33 +0,0 @@
-{
-  "meta": {
-    "id": "workbench",
-    "version": "2.0.0",
-    "parent": "base",
-    "description": "High density technical interface skin"
-  },
-  "tokens": {
-    "colors": {
-      "primary": "#2563EB",
-      "secondary": "#475569",
-      "danger": "#DC2626",
-      "background": "#0F172A",
-      "surface": "#1E293B",
-      "text": "#E2E8F0"
-    },
-    "spacing": {
-      "1": "2px",
-      "2": "4px",
-      "4": "8px",
-      "8": "16px"
-    },
-    "borderRadius": {
-      "default": "0px",
-      "lg": "2px"
-    },
-    "typography": {
-      "fontFamily": {
-        "sans": ["Inter", "system-ui", "sans-serif"]
-      }
-    }
-  }
-}