feat: redesign admin settings with tree navigation and compact layout

- Replace flat sidebar with collapsible tree groups (7 groups, 52 sub-items)
- Map all 61 backend category keys to sidebar navigation
- Add QuickToggles panel for boolean settings
- Replace card-style SettingRow with compact SettingsTableRow
- Add breadcrumb navigation for tree sub-items
- Add source badges (modified/DB/ENV) on settings
- Implement two-level mobile navigation with group chips
- Add i18n translations for all new keys (en, ru, zh, fa)

src/locales/en.json

@@ -1836,8 +1836,11 @@
       "title": "System Settings",
       "allCategories": "All categories",
       "noSettings": "No settings found",
+      "quickToggles": "Quick Toggles",
       "modified": "Modified",
       "readOnly": "Read only",
+      "badgeDb": "DB",
+      "badgeEnv": "ENV",
       "reset": "Reset",
       "categoriesCount": "categories",
       "settingsCount": "settings",
@@ -1910,6 +1913,84 @@
       "quickPresets": "Quick presets",
       "resetAllColors": "Reset all colors",
       "statusColors": "Status colors",
+      "favorites": "Favorites",
+      "branding": "Branding",
+      "theme": "Theme",
+      "payments": "Payments",
+      "subscriptions": "Subscriptions",
+      "interface": "Interface",
+      "notifications": "Notifications",
+      "database": "Database",
+      "system": "System",
+      "users": "Users",
+      "customization": "Customization",
+      "settingsLabel": "Settings",
+      "backToAdmin": "Back to admin",
+      "totalCount": "{{count}} total",
+      "modifiedCount": "{{count}} modified",
+      "groups": {
+        "payments": "Payments",
+        "subscriptions": "Subscriptions",
+        "interface": "Interface",
+        "users": "Users",
+        "notifications": "Notifications",
+        "database": "Database",
+        "system": "System"
+      },
+      "tree": {
+        "payments_general": "General",
+        "payments_stars": "Telegram Stars",
+        "payments_yookassa": "YooKassa",
+        "payments_cryptobot": "CryptoBot",
+        "payments_cloudpayments": "CloudPayments",
+        "payments_freekassa": "FreeKassa",
+        "payments_kassa_ai": "Kassa AI",
+        "payments_platega": "Platega",
+        "payments_pal24": "PAL24",
+        "payments_heleket": "Heleket",
+        "payments_mulenpay": "MulenPay",
+        "payments_tribute": "Tribute",
+        "payments_wata": "Wata",
+        "payments_riopay": "RioPay",
+        "payments_severpay": "SeverPay",
+        "subs_core": "Core",
+        "subs_trial": "Trial",
+        "subs_pricing": "Pricing",
+        "subs_periods": "Periods",
+        "subs_traffic": "Traffic",
+        "subs_simple": "Simple subscription",
+        "subs_autopay": "Auto-pay",
+        "iface_general": "General",
+        "iface_connect": "Connect button",
+        "iface_miniapp": "MiniApp",
+        "iface_happ": "HAPP",
+        "iface_widget": "Login Widget",
+        "iface_oidc": "OIDC",
+        "iface_skip": "Skip steps",
+        "iface_additional": "Additional",
+        "users_support": "Support",
+        "users_referral": "Referral",
+        "users_channel": "Channel",
+        "users_localization": "Localization",
+        "users_moderation": "Moderation",
+        "notif_user": "User notifications",
+        "notif_admin": "Admin notifications",
+        "notif_reports": "Reports",
+        "db_general": "General",
+        "db_postgres": "PostgreSQL",
+        "db_sqlite": "SQLite",
+        "db_redis": "Redis",
+        "sys_core": "Core & Debug",
+        "sys_remnawave": "RemnaWave",
+        "sys_webapi": "Web API",
+        "sys_webhook": "Webhook",
+        "sys_server": "Server status",
+        "sys_monitoring": "Monitoring",
+        "sys_maintenance": "Maintenance",
+        "sys_backup": "Backup",
+        "sys_version": "Version",
+        "sys_logging": "Logging"
+      },
       "categories": {
         "TELEGRAM_WIDGET": "Telegram Login Widget",
         "TELEGRAM_OIDC": "Telegram Login (OIDC)"