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/cli-workflow/src/cli.ts

@@ -45,7 +45,9 @@ function runAction(action: () => Promise<void>): void {
 
 const program = new Command();
 
-program.name("uwf").description("Stateless workflow CLI");
+// eslint-disable-next-line -- dynamic import for version
+const pkg = await import("../package.json", { with: { type: "json" } });
+program.name("uwf").description("Stateless workflow CLI").version(pkg.default.version, "-V, --version");
 program.option("--format <fmt>", "Output format: json or yaml", "json");
 
 const workflow = program.command("workflow").description("Workflow registry and CAS");