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/cmd/server/main.go

@@ -369,6 +369,8 @@ func main() {
 	mux.HandleFunc("POST /ingest-path", h.IngestPath)
 	mux.HandleFunc("POST /ingest-raw", h.IngestRaw)
 	mux.HandleFunc("POST /backfill-refs", h.BackfillRefs)
+	mux.HandleFunc("GET /pending", h.Pending)
+	mux.HandleFunc("POST /promote", h.Promote)
 	mux.HandleFunc("POST /backfill-embeddings", h.BackfillEmbeddings)
 	mux.HandleFunc("GET /pass-rate", h.PassRate)
 	jwtValidator, err := chassisauth.NewJWTValidator(ctx, os.Getenv("DEX_ISSUER_URL"), os.Getenv("MCP_AUDIENCE"))