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/packages/flow/src/gateway/dispatch/serialize.ts

@@ -229,6 +229,7 @@ function deepInternalToClient(value: unknown): unknown {
 const TERM_BEARING_REQUEST_SERVICES = new Set([
   "triples",
   "knowledge",
+  "librarian",
 ]);
 
 /**
@@ -238,6 +239,7 @@ const TERM_BEARING_RESPONSE_SERVICES = new Set([
   "triples",
   "graph-embeddings",
   "knowledge",
+  "librarian",
 ]);
 
 // ---------- Top-level request / response translators ----------