feat/139-thread-reactor
main
- Rewrite supervisor to use createThreadReactor + createLlmFn - No direct fetch/HTTP calls in supervisor - All 266 tests passing Refs #139, relates #141
- New src/reactor/ module: createThreadReactor, createLlmFn, types - Two-stage API: config (llm, systemPrompt, tools, toolHandler) + per-call (thread, input, schema) - All tool failures are recoverable (returned to LLM as error message) - Rewrite createExtract to use createThreadReactor - Delete reactExtract old implementation - Fix template test imports (START/END from runtime, validateWorkflowDescriptor from engine) 268 tests passing. Refs #139, relates #140