feat(dns+ntp): DNS-Cache-Flush + NTP-Force-Sync — operative Aktionen (1.1.94)

Backend: POST /dns/flush-cache (unbound-control flush_zone .)
         POST /ntp/force-sync  (chronyc makestep)
Beide werden im Audit-Log festgehalten.
UI: Schaltflächen in DNS-Settings und NTP-Settings neben Save,
    mit Tooltip-Beschreibung + i18n (de+en).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

management-ui/src/i18n/locales/en/common.json

@@ -838,7 +838,11 @@
       "rtcsync": "Sync RTC with system time",
       "rtcsyncExtra": "Keep hardware clock in sync every 11 min — after reboot time is roughly correct.",
       "leapsectz": "Leap-sec TZ",
-      "leapsectzExtra": "Optional, e.g. 'right/UTC' for leap-sec via tzdata."
+      "leapsectzExtra": "Optional, e.g. 'right/UTC' for leap-sec via tzdata.",
+      "forceSyncBtn": "Force clock step",
+      "forceSyncTooltip": "Immediately step the system clock to the NTP reference (chronyc makestep). Use after VM migration or long outage.",
+      "forceSyncOk": "Clock stepped successfully",
+      "forceSyncFailed": "Force sync failed"
     }
   },
   "dns": {
@@ -892,7 +896,11 @@
       "cacheMax": "Cache max-TTL",
       "allIPv4": "all IPv4 interfaces",
       "allIPv6": "all IPv6 interfaces",
-      "loopback": "Loopback"
+      "loopback": "Loopback",
+      "flushCacheBtn": "Flush DNS cache",
+      "flushCacheTooltip": "Discard all cached records (unbound-control flush_zone .). Use after DNS changes have propagated.",
+      "flushCacheOk": "DNS cache flushed",
+      "flushCacheFailed": "Flush failed"
     }
   },
   "fwd": {