refactor: extract @uncaged/workflow-util-agent + smart prompt

- New package: spawn-cli + build-agent-prompt shared utils
- Smart prompt: start + meta summaries for middle steps + last step full
- Cursor/Hermes adapters now import from util-agent (no duplicate code)
- 109 tests pass, biome clean

Closes #14
小橘 <xiaoju@shazhou.work>

tsconfig.json

@@ -22,6 +22,7 @@
     { "path": "packages/workflow-role-reviewer" },
     { "path": "packages/workflow-agent-cursor" },
     { "path": "packages/workflow-agent-hermes" },
+    { "path": "packages/workflow-util-agent" },
     { "path": "packages/cli-workflow" },
     { "path": "packages/workflow-template-solve-issue" }
   ]