feat(mcp): brain_pending + brain_promote tools + REST routes (#38)

Wires the curation primitives into the MCP surface (all three sites:
tools() descriptors, handleCall dispatch, package doc) and registers the
GET /pending + POST /promote REST routes. brain_promote additionally
re-indexes the promoted note into the graph (best-effort), matching the
other write paths. brain_pending is the human-review-queue complement to
the agent-facing brain_write.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ingestion/internal/mcp/server.go

@@ -1,8 +1,9 @@
 // Package mcp implements an MCP HTTP handler for the ingestion service.
 // Exposed tools: brain_query, brain_write, brain_update, brain_get,
-// brain_index, brain_tunnel, brain_ingest, brain_ingest_raw,
-// brain_answer, brain_classify, brain_graph, brain_context, session_log,
-// and capture (the #55 relay tool, registered only when WithCapture is set).
+// brain_pending, brain_promote, brain_index, brain_tunnel, brain_ingest,
+// brain_ingest_raw, brain_answer, brain_classify, brain_graph,
+// brain_context, session_log, and capture (the #55 relay tool, registered
+// only when WithCapture is set).
 package mcp
 
 import (
@@ -263,6 +264,10 @@ func (s *Server) handleCall(ctx context.Context, name string, args json.RawMessa
 		return s.brainUpdate(ctx, args)
 	case "brain_get":
 		return s.brainGet(ctx, args)
+	case "brain_pending":
+		return s.brainPending(ctx, args)
+	case "brain_promote":
+		return s.brainPromote(ctx, args)
 	case "capture":
 		return s.brainCapture(ctx, args)
 	case "brain_index":