feat(control-center): P2 document vector store — ingestion, chunking, embedding, hybrid search

- internal/controlcenter/embed: OpenAI-compatible /embeddings client
  (batch<=16, 30s timeout, 5xx/network retried once, 4xx not), Embedder
  interface, deterministic offline Stub, pgvector literal formatting
- internal/controlcenter/docs: .doc/**/*.md sync into cc_documents with
  sha256 diffing and vanished-file removal; YAML front matter -> jsonb,
  title fallback, taxonomy from first .doc dir; heading-based chunking
  with paragraph bisection over ~1800 est. tokens; chunk_hash idempotent
  inserts (unchanged chunks keep embeddings); embedding failures degrade
  to NULL vectors without failing the sync; IndexArtifact for
  cc_stage_artifacts; StartPeriodic ticker (CC_DOC_SYNC_SECONDS)
- server: GET /api/v1/docs (taxonomy/q filters), /api/v1/docs/{id},
  /api/v1/docs/search (semantic|keyword|hybrid, ts_rank+ILIKE keyword
  fallback, 0.6/0.4 max-normalized fusion, degraded flag when embedding
  unavailable); async artifact indexing hooked into agent artifacts and
  external-submit handlers
- archtest module-boundaries allowlist updated for new packages

cmd/control-center/main.go

@@ -16,6 +16,8 @@ import (
 	"time"
 
 	"chat-agent-system/internal/controlcenter/config"
+	"chat-agent-system/internal/controlcenter/docs"
+	"chat-agent-system/internal/controlcenter/embed"
 	"chat-agent-system/internal/controlcenter/server"
 	"chat-agent-system/internal/controlcenter/store"
 )
@@ -77,6 +79,23 @@ func cmdServe(args []string) error {
 	}
 	srv := server.New(cfg, st)
 
+	var emb *embed.HTTPClient
+	if cfg.EmbeddingEndpoint != "" {
+		emb = embed.NewHTTP(cfg.EmbeddingEndpoint, cfg.EmbeddingAPIKey, cfg.EmbeddingModel, embed.Dim)
+	} else {
+		slog.Warn("embedding endpoint not configured; search runs keyword-only")
+	}
+	syncer := docs.New(st, cfg.RepoRoot, emb)
+	var embIface embed.Embedder
+	if emb != nil {
+		embIface = emb
+	}
+	srv.SetDocs(embIface, syncer)
+
+	syncCtx, stopSync := context.WithCancel(ctx)
+	defer stopSync()
+	syncer.StartPeriodic(syncCtx, time.Duration(cfg.DocSyncSecond)*time.Second)
+
 	reapCtx, stopReaper := context.WithCancel(ctx)
 	defer stopReaper()
 	srv.StartLeaseReaper(reapCtx)
@@ -86,6 +105,7 @@ func cmdServe(args []string) error {
 		sig := make(chan os.Signal, 1)
 		signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
 		<-sig
+		stopSync()
 		stopReaper()
 		shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 		defer cancel()