docs: Phase 20 T5 — wire ClusterReplicationMode into diagnostic surface

Add ClusterReplicationMode and EngineProjectionMode to
FailoverVolumeState so each volume in the failover diagnostic
carries its cluster/engine mode at diagnosis time.

FailoverDiagnosticSnapshot() enriches volume entries by looking up
the registry entry for each volume. This covers both the block
volume API (GET /block/volume/{name}) and the failover diagnostic
snapshot surface.

Update phase doc to reflect actual exposure paths.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

weed/server/master_block_failover.go

@@ -40,12 +40,14 @@ type blockFailoverState struct {
 
 // FailoverVolumeState is one volume's failover diagnosis entry.
 type FailoverVolumeState struct {
-	VolumeName       string
-	CurrentPrimary   string
-	AffectedServer   string // dead server that triggered the failover/rebuild
-	DeferredPromotion bool  // true if a deferred promotion timer is pending
-	PendingRebuild   bool  // true if a rebuild is pending for this volume
-	Reason           string // "lease_wait", "rebuild_pending", or ""
+	VolumeName             string
+	CurrentPrimary         string
+	AffectedServer         string // dead server that triggered the failover/rebuild
+	DeferredPromotion      bool   // true if a deferred promotion timer is pending
+	PendingRebuild         bool   // true if a rebuild is pending for this volume
+	Reason                 string // "lease_wait", "rebuild_pending", or ""
+	ClusterReplicationMode string // T5: cluster-level RF2 health at diagnosis time
+	EngineProjectionMode   string // T1: VS-local engine projection at diagnosis time
 }
 
 // FailoverDiagnostic is a bounded read-only snapshot of failover state
@@ -106,6 +108,15 @@ func (ms *MasterServer) FailoverDiagnosticSnapshot() FailoverDiagnostic {
 	default:
 		diag.V2PromotionMode = "placeholder_fail_closed"
 	}
+	// T5: enrich each volume entry with cluster/engine mode from registry.
+	if ms.blockRegistry != nil {
+		for i := range diag.Volumes {
+			if entry, ok := ms.blockRegistry.Lookup(diag.Volumes[i].VolumeName); ok {
+				diag.Volumes[i].ClusterReplicationMode = entry.ClusterReplicationMode
+				diag.Volumes[i].EngineProjectionMode = entry.EngineProjectionMode
+			}
+		}
+	}
 	return diag
 }