fix(node): fully delete clients on nodes instead of only detaching them

Deleting a client on the master propagated to nodes via the detach
endpoint, which removes the client from that one inbound's settings but
deliberately keeps the client record. The node ended up with an
orphaned record that kept showing in its Clients view; the master and
node could never converge on a delete.

Full-delete and detach intent now travel separately: the Runtime
interface gains DeleteClient, which on Remote hits the node's
panel/api/clients/del endpoint (record, attachments, traffic; repeat
calls for a client on several inbounds of the same node are swallowed
as idempotent "not found"). Delete/DeleteByEmail/BulkDelete use it for
node inbounds, while Detach/BulkDetach keep the inbound-scoped detach
RPC so removing a client from one inbound never wipes it node-wide
(the #5543 guarantee is preserved and covered by tests). Bulk deletes
above the fold threshold still converge membership via reconcile; their
leftover node records can be cleaned with the node's delete-orphans
action.

Closes #5797

internal/web/runtime/runtime.go

@@ -23,6 +23,13 @@ type Runtime interface {
 	DeleteUser(ctx context.Context, ib *model.Inbound, email string) error
 	AddClient(ctx context.Context, ib *model.Inbound, client model.Client) error
 
+	// DeleteClient removes the client identified by email entirely from the
+	// runtime's own store: on Remote it hits the node's full-delete endpoint
+	// (record, attachments, traffic), unlike DeleteUser which only detaches
+	// from one inbound and leaves the node's client record behind. Local has
+	// no client store of its own, so it is a no-op there.
+	DeleteClient(ctx context.Context, email string) error
+
 	RestartXray(ctx context.Context) error
 
 	ResetClientTraffic(ctx context.Context, ib *model.Inbound, email string) error