feat: make each plugin an npm workspace built by a termix-plugin CLI

plugins/workspaces/manifest.json

@@ -15,8 +15,6 @@
     "api": "1"
   },
   "capabilities": ["db:own", "ui:surface"],
-  "backend": "backend/index.mjs",
-  "frontend": "frontend/index.mjs",
   "locales": "locales",
   "platforms": ["linux", "win32", "darwin"]
 }