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/sse.ts

@@ -7,7 +7,7 @@
 
 // ── Types ──────────────────────────────────────────────────────────
 
-export type SSEEventType = 'deploy_log' | 'instance_status' | 'deploy_status';
+export type SSEEventType = 'deploy_log' | 'instance_status' | 'deploy_status' | 'event_log';
 
 export interface SSEEvent<T = unknown> {
 	type: SSEEventType;
@@ -36,7 +36,16 @@ export interface DeployStatusPayload {
 	error?: string;
 }
 
-type SSEPayload = DeployLogPayload | InstanceStatusPayload | DeployStatusPayload;
+export interface EventLogSSEPayload {
+	id: number;
+	source: string;
+	severity: string;
+	message: string;
+	metadata: string;
+	created_at: string;
+}
+
+type SSEPayload = DeployLogPayload | InstanceStatusPayload | DeployStatusPayload | EventLogSSEPayload;
 
 export interface SSEOptions {
 	/** Called for each SSE event received. */
@@ -179,6 +188,7 @@ export function connectDeployLogs(
 export function connectGlobalEvents(callbacks: {
 	onInstanceStatus?: (payload: InstanceStatusPayload) => void;
 	onDeployStatus?: (payload: DeployStatusPayload) => void;
+	onEventLog?: (payload: EventLogSSEPayload) => void;
 	onOpen?: () => void;
 	onError?: (attempt: number) => void;
 }): SSEConnection {
@@ -188,6 +198,8 @@ export function connectGlobalEvents(callbacks: {
 				callbacks.onInstanceStatus?.(event.payload as InstanceStatusPayload);
 			} else if (event.type === 'deploy_status') {
 				callbacks.onDeployStatus?.(event.payload as DeployStatusPayload);
+			} else if (event.type === 'event_log') {
+				callbacks.onEventLog?.(event.payload as EventLogSSEPayload);
 			}
 		},
 		onOpen: callbacks.onOpen,