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-role-committer/src/committer.ts

@@ -32,4 +32,5 @@ export const committerRole: RoleDefinition<CommitterMeta> = {
     "Extract the commit result: committed (with branch and SHA), recoverable failure, or unrecoverable failure. Include error details and log references if applicable.",
   schema: committerMetaSchema,
   extractRefs: null,
+  extractMode: "single",
 };