Fix CI build order: build core before dependent packages

npm run build --workspaces runs packages in parallel, causing
adapter-claude, bunshin, and demo to fail when core hasn't built yet.
Replaced with explicit three-phase build: core → middleware packages → demo.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: wharfe

package.json

@@ -5,7 +5,7 @@
     "packages/*"
   ],
   "scripts": {
-    "build": "npm run build --workspaces",
+    "build": "npm run build -w packages/core && npm run build -w packages/adapter-claude -w packages/bunshin -w packages/plugin-minesweeper && npm run build -w packages/demo",
     "typecheck": "npm run typecheck --workspaces",
     "test": "npm test --workspaces --if-present",
     "changeset": "changeset",