feat: add document pipeline, ReAct agent, and knowledge core services

Document Pipeline (Team A):
- LibrarianService: document storage with filesystem backend, metadata
  persistence, child document hierarchy, collection management
- ChunkingService: recursive character text splitter with configurable
  chunk size/overlap, FlowProcessor pattern
- KnowledgeExtractService: combined relationship + definition extraction
  using prompt service and LLM, emits RDF triples and entity contexts
- KnowledgeCoreService: knowledge core CRUD with streaming export and
  flow-based loading

ReAct Agent (Team B):
- StreamingReActParser: state machine for parsing LLM output into
  Thought/Action/ActionInput/FinalAnswer sections
- Three MVP tools: KnowledgeQuery (GraphRAG), DocumentQuery (DocRAG),
  TriplesQuery with RequestResponse clients
- AgentService FlowProcessor with ReAct loop, tool execution, and
  streaming chunk responses (thought/observation/answer)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ts/scripts/run-librarian.ts

@@ -0,0 +1,15 @@
+/**
+ * Start the librarian service.
+ *
+ * Usage: pnpm tsx scripts/run-librarian.ts
+ *
+ * Env:
+ *   NATS_URL           (default: nats://localhost:4222)
+ *   LIBRARIAN_DATA_DIR (optional, e.g., ./data/librarian)
+ */
+import { run } from "../packages/flow/src/librarian/service.js";
+
+run().catch((err) => {
+  console.error("Librarian service failed:", err);
+  process.exit(1);
+});