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/base.json

@@ -1,28 +0,0 @@
-{
-  "meta": {
-    "id": "base",
-    "version": "1.0.0",
-    "description": "Foundation tokens shared across all skins"
-  },
-  "tokens": {
-    "colors": {
-      "transparent": "transparent",
-      "current": "currentColor",
-      "white": "#ffffff",
-      "black": "#000000"
-    },
-    "spacing": {
-      "0": "0px",
-      "1": "4px",
-      "2": "8px",
-      "4": "16px",
-      "8": "32px"
-    },
-    "typography": {
-      "fontFamily": {
-        "sans": ["system-ui", "sans-serif"],
-        "mono": ["monospace"]
-      }
-    }
-  }
-}