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/integrations/onlyoffice_nextcloud.go

@@ -3,8 +3,8 @@ package integrations
 import (
 	"context"
 	"fmt"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/dockerexec"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/util"
-	"os/exec"
 	"strings"
 	"time"
 )
@@ -67,7 +67,7 @@ func (h *OnlyOfficeNextcloudHandler) Apply(ac *ApplyContext) error {
 
 	for _, cmd := range commands {
 		ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-		c := exec.CommandContext(ctx, cmd.args[0], cmd.args[1:]...)
+		c := dockerexec.CommandContext(ctx, cmd.args[0], cmd.args[1:]...)
 		out, err := c.CombinedOutput()
 		cancel()
 		if err != nil {
@@ -89,7 +89,7 @@ func (h *OnlyOfficeNextcloudHandler) Revoke(ac *ApplyContext) error {
 	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
 	defer cancel()
 
-	cmd := exec.CommandContext(ctx, "docker", "exec", "-u", "www-data", "nextcloud", "php", "occ", "app:disable", "onlyoffice")
+	cmd := dockerexec.CommandContext(ctx, "docker", "exec", "-u", "www-data", "nextcloud", "php", "occ", "app:disable", "onlyoffice")
 	out, err := cmd.CombinedOutput()
 	if err != nil {
 		outStr := string(out)