feat: ReAct ExtractFn with tool-use

- RoleDefinition.extractMode: "single" | "react"
- reactExtract: multi-turn LLM with cas_get tool for DAG traversal
- Max 10 tool-call rounds, schema validation on final output
- create-workflow routes to reactExtract when extractMode is "react"
- All existing roles set to "single" (no behavior change)
- 162 tests passing

Fixes #44

packages/workflow/src/index.ts

@@ -54,6 +54,7 @@ export {
   serializeMerkleNode,
   type ThreadMerklePayload,
 } from "./merkle.js";
+export { type ReactExtractArgs, reactExtract } from "./react-extract.js";
 export {
   type ExtractProviderConfig,
   getRegisteredWorkflow,
@@ -80,6 +81,7 @@ export {
   type AgentFn,
   END,
   type ExtractContext,
+  type ExtractMode,
   type LlmProvider,
   type Moderator,
   type ModeratorContext,