chore(bit-by-bit): enable frontend-design plugin

Adds .claude/settings.json opting bit-by-bit into the frontend-design
plugin for future UI/design work on the pixel-art tracker.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

bit-by-bit/.claude/settings.json

@@ -0,0 +1,5 @@
+{
+  "enabledPlugins": {
+    "frontend-design@claude-plugins-official": true
+  }
+}