feat(dashboard): more System History metrics, persistence & localized labels

- Sample swap %, TCP/UDP connection counts and disk-usage % on the host ticker
- System History: Swap overlaid on the RAM tab, plus new Connections and Disk Usage tabs
- Persist the host time-series across restarts: gob snapshot beside the DB, written on a timer and at shutdown, restored on boot
- Live-refresh the open chart (2s for short ranges, 10s for longer)
- Localize CPU/RAM/Swap and the new tab/chart titles across all 13 languages and route legend series names through i18n

web/translation/fa-IR.json

@@ -128,12 +128,12 @@
     },
     "index": {
       "title": "نمای کلی",
-      "cpu": "CPU",
+      "cpu": "پردازنده",
       "logicalProcessors": "پردازنده‌های منطقی",
       "frequency": "فرکانس",
-      "swap": "Swap",
+      "swap": "سواپ",
       "storage": "ذخیره‌سازی",
-      "memory": "RAM",
+      "memory": "حافظه",
       "threads": "نخ‌ها",
       "xrayStatus": "Xray",
       "stopXray": "توقف",
@@ -162,11 +162,15 @@
       "historyTitleDisk": "ورودی/خروجی دیسک",
       "historyTitleOnline": "کاربران آنلاین",
       "historyTitleLoad": "میانگین بار سیستم (۱ / ۵ / ۱۵ دقیقه)",
+      "historyTitleConnections": "اتصالات فعال (TCP / UDP)",
+      "historyTitleDiskUsage": "مصرف فضای دیسک",
       "historyTabBandwidth": "پهنای باند",
       "historyTabPackets": "بسته‌ها",
-      "historyTabDisk": "Disk I/O",
+      "historyTabDisk": "دیسک I/O",
       "historyTabOnline": "آنلاین",
       "historyTabLoad": "بار",
+      "historyTabConnections": "اتصالات",
+      "historyTabDiskUsage": "مصرف دیسک",
       "charts": "نمودارها",
       "xrayMetricsTitle": "متریک‌های Xray",
       "xrayTitleHeap": "حافظه‌ی Heap تخصیص‌یافته",