docker: remove images no container or declaration uses, keeping the previous of each line (hq ADR 0251)

Images pulled by digest are not dangling, so the weekly prune never takes an old version
and every machine keeps every image it ever ran. docker_prune_images takes them, keeps what
the declaration names (asked of the controller; no answer, nothing removed) and the one before,
and is a dry run unless asked with a why.

modules/docker/cmd/docker-tools/docker.go

@@ -20,6 +20,8 @@ import (
 	"strconv"
 	"strings"
 	"time"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
 )
 
 // MeshLabel is the label the host puts on every container it creates (mesh-host internal/apply).
@@ -34,11 +36,14 @@ type Client struct {
 	UID      int
 	ReadFile func(string) ([]byte, error)
 	Now      func() time.Time
+	// Ask asks the mesh (the SDK's stdio.Ask); Node is this machine's name (MESH_NODE).
+	Ask  Asker
+	Node string
 }
 
 // NewClient is the client the bundle serves with.
 func NewClient() *Client {
-	return &Client{Run: ExecRunner, UID: os.Getuid(), ReadFile: os.ReadFile, Now: time.Now}
+	return &Client{Run: ExecRunner, UID: os.Getuid(), ReadFile: os.ReadFile, Now: time.Now, Ask: stdio.Ask, Node: os.Getenv("MESH_NODE")}
 }
 
 var socketRefused = regexp.MustCompile(`(?i)permission denied.*docker.*sock|docker\.sock.*permission denied`)