feat(observability): phases 4-7 - complete frontend UI (big bang)

Add all frontend pages for observability & proxy management:
- Proxy Viewer: /proxies with grouped view, filtering, health indicators
- Proxy Creation: form with live validation, diagnostic hints, edit/delete
- Stale Containers: /containers/stale with dashboard widget, cleanup actions
- Event Log: /events with filters, pagination, real-time SSE streaming
- Navigation: proxies and events links in sidebar
- i18n: full EN/RU translations for all new features
- Settings: stale threshold configuration

web/src/lib/i18n/en.json

@@ -7,6 +7,8 @@
     "dashboard": "Dashboard",
     "projects": "Projects",
     "deploy": "Deploy",
+    "proxies": "Proxies",
+    "events": "Events",
     "settings": "Settings"
   },
   "dashboard": {
@@ -19,7 +21,8 @@
     "retry": "Retry",
     "noProjects": "No projects yet.",
     "addFirst": "Add your first project",
-    "loadFailed": "Failed to load dashboard"
+    "loadFailed": "Failed to load dashboard",
+    "staleContainers": "Stale Containers"
   },
   "projects": {
     "title": "Projects",
@@ -176,7 +179,9 @@
     "registries": "Registries",
     "credentials": "Credentials",
     "authentication": "Authentication",
-    "appearance": "Appearance"
+    "appearance": "Appearance",
+    "staleThreshold": "Stale threshold (days)",
+    "staleThresholdHelp": "Containers inactive for longer than this will be flagged as stale."
   },
   "settingsGeneral": {
     "title": "General Settings",
@@ -320,6 +325,27 @@
     "loginFailed": "Login failed",
     "networkError": "Network error"
   },
+  "proxies": {
+    "title": "Proxy Manager",
+    "create": "Create Proxy",
+    "standalone": "Standalone Proxies",
+    "managed": "Managed Proxies",
+    "noProxies": "No proxies found",
+    "noProxiesDesc": "Create a standalone proxy or deploy a project with proxy enabled.",
+    "filter": {
+      "search": "Search by domain or destination...",
+      "health": "Health",
+      "type": "Type",
+      "all": "All",
+      "clear": "Clear filters"
+    },
+    "health": {
+      "healthy": "Healthy",
+      "unhealthy": "Unhealthy",
+      "unknown": "Unknown"
+    },
+    "lastChecked": "Last checked"
+  },
   "common": {
     "cancel": "Cancel",
     "confirm": "Confirm",
@@ -387,6 +413,97 @@
     "search": "Search...",
     "noResults": "No results found"
   },
+  "stale": {
+    "title": "Stale Containers",
+    "noStale": "No stale containers",
+    "noStaleDesc": "All containers are healthy and running.",
+    "cleanup": "Clean up",
+    "cleanupAll": "Clean up all",
+    "confirmCleanup": "This will stop and remove the container. Continue?",
+    "confirmBulkCleanup": "This will stop and remove all stale containers. Continue?",
+    "daysStale": "days stale",
+    "lastAlive": "Last alive",
+    "count": "Stale",
+    "cleanedUp": "Container cleaned up",
+    "bulkCleanedUp": "{count} containers cleaned up",
+    "cleanupFailed": "Cleanup failed",
+    "loadFailed": "Failed to load stale containers"
+  },
+  "proxies": {
+    "title": "Proxies",
+    "create": "Create Proxy",
+    "noProxies": "No proxies configured yet.",
+    "noProxiesDesc": "Create a standalone proxy or deploy a project to see proxies here.",
+    "standalone": "Standalone Proxies",
+    "managed": "Managed",
+    "lastChecked": "Last checked",
+    "health": {
+      "healthy": "Healthy",
+      "unhealthy": "Unhealthy",
+      "unknown": "Unknown"
+    },
+    "filter": {
+      "search": "Search proxies...",
+      "health": "Health",
+      "type": "Type",
+      "all": "All",
+      "clear": "Clear filters"
+    },
+    "form": {
+      "title": "Create Proxy",
+      "editTitle": "Edit Proxy",
+      "destination": "Destination URL / IP",
+      "port": "Port",
+      "domain": "Domain",
+      "domainHelp": "The public domain for this proxy.",
+      "validate": "Validate",
+      "validating": "Validating...",
+      "create": "Create Proxy",
+      "save": "Save Changes",
+      "cancel": "Cancel",
+      "delete": "Delete",
+      "deleteConfirm": "Delete this proxy? This cannot be undone."
+    },
+    "validation": {
+      "title": "Destination Validation",
+      "syntax": "URL syntax",
+      "dns": "DNS resolution",
+      "tcp": "TCP connection",
+      "http": "HTTP response",
+      "checking": "Checking...",
+      "skipped": "Skipped"
+    }
+  },
+  "events": {
+    "title": "Event Log",
+    "noEvents": "No events found",
+    "noEventsDesc": "Events will appear here as they occur.",
+    "loadMore": "Load more",
+    "newEvents": "new events",
+    "filter": {
+      "severity": "Severity",
+      "source": "Source",
+      "dateRange": "Date range",
+      "search": "Search events...",
+      "lastHour": "Last hour",
+      "last24h": "Last 24 hours",
+      "last7d": "Last 7 days",
+      "allTime": "All time",
+      "clear": "Clear filters"
+    },
+    "severity": {
+      "info": "Info",
+      "warn": "Warning",
+      "error": "Error"
+    },
+    "source": {
+      "deploy": "Deploy",
+      "container": "Container",
+      "proxy": "Proxy",
+      "system": "System"
+    },
+    "metadata": "Details"
+  },
   "language": {
     "en": "English",
     "ru": "Russian"