controller v0.267.0: tests off DooPlex's Docker, cut-off copies refused, two pages true

R-650: internal/dockerexec — every docker exec routed through it; under
go test a real docker is refused (opt-in FELHOM_TEST_REAL_DOCKER=1; a stub
under the temp dir is allowed). api/stacks/web tests run under a silent
stub (TestMain). TestR650_NoBareDockerExec pins it repo-wide.
R-640: a dump without its engine's completion marker is refused before
the first mutation (unit + off-site restore) and again before any load.
R-499: the Tier-2 page's system-disk sentence has four true branches.
R-518: the backup button states the measured ~8 min stop.
R-626: measured on 9202, not reproduced.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/stacks/installed.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/dockerexec"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -32,7 +33,7 @@ const installedRecordTimeout = 30 * time.Second
 type execRunner func(ctx context.Context, dir string, env []string, name string, args ...string) (string, error)
 
 func defaultExecRunner(ctx context.Context, dir string, env []string, name string, args ...string) (string, error) {
-	cmd := exec.CommandContext(ctx, name, args...)
+	cmd := dockerexec.CommandContext(ctx, name, args...)
 	if dir != "" {
 		cmd.Dir = dir
 	}