feat: M3 peer gossip protocol

Refs #1

- peers table (peer_id, addr, cursor, last_handshake)
- watch serves HTTP API: GET /v1/ping (knowledge vector),
  GET /v1/log?node=&after= (cursor-paged pull), POST /v1/obs/batch
- anti-entropy sweep (Run): ping, pull what we lack, push own obs;
  echo suppressed by node_id ownership; reconcile-on-pull
- config via KNOX_PEERS / KNOX_PEER_ADDR; knox gossip status
- db: GossipObservation wire type, PushObservations, ObservationsAfter,
  KnowledgeVector, peer upsert/list
- integration tests: bidirectional convergence + idempotency

internal/cmd/reconcile.go

@@ -26,27 +26,18 @@ observations it now holds.`,
 			if dryRun {
 				return dryRunReconcile(kdb)
 			}
-			return reconcile(kdb)
+			created, linked, err := watch.Reconcile(kdb)
+			if err != nil {
+				return err
+			}
+			fmt.Printf("reconciled: entries rebuilt, %d threads created, %d observations linked\n", created, linked)
+			return nil
 		},
 	}
 	cmd.Flags().BoolVar(&dryRun, "dry-run", false, "report drift without writing")
 	return cmd
 }
 
-func reconcile(kdb *db.KnoxDB) error {
-	before, after, err := kdb.RebuildEntriesFromObservations()
-	if err != nil {
-		return fmt.Errorf("rebuild entries: %w", err)
-	}
-	threader := watch.NewAutoThreader(kdb)
-	created, linked, err := threader.AutoThread()
-	if err != nil {
-		return fmt.Errorf("auto-thread: %w", err)
-	}
-	fmt.Printf("reconciled: entries %d -> %d, %d threads created, %d observations linked\n", before, after, created, linked)
-	return nil
-}
-
 func dryRunReconcile(kdb *db.KnoxDB) error {
 	// Ground truth from the log (computed in a throwaway way via a count of
 	// what rebuild would produce) vs the current materialized cache.