feat: add four-phase role description (identity/prepare/execute/report)

- Extend RoleDefinition with identity, prepare, execute, report fields
- Make systemPrompt optional (nullable) for four-phase workflows
- Update ROLE_DEFINITION JSON Schema (all new fields optional)
- Update validate.ts to accept new fields
- Update workflow.ts to strip null fields before CAS storage
- Update thread read to prefer identity over systemPrompt
- Add --version flag to uwf CLI
- Bump all packages to 0.5.0

Refs #359

packages/workflow-protocol/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@uncaged/workflow-protocol",
-  "version": "0.1.0",
+  "version": "0.5.0",
   "files": [
     "src",
     "dist",