init: bun workspace + RFC-001 workflow engine design

- @uncaged/workflow (core lib) + @uncaged/cli-workflow (CLI)
- RFC-001: full design doc covering storage, threading, CLI

小橘 <xiaoju@shazhou.work>

package.json

@@ -0,0 +1,9 @@
+{
+  "name": "@uncaged/workflow-monorepo",
+  "private": true,
+  "workspaces": ["packages/*"],
+  "scripts": {
+    "build": "bun run --filter '*' build",
+    "test": "bun run --filter '*' test"
+  }
+}