Add egress state and probe service (#3937)

Adds the EgressService that probes a configurable set of reliability targets
(ping, TCP or HTTP) when asked, persists a single instance-wide egress state
document, and runs a recovery poll loop while egress is degraded. Adds the four
egress settings fields with validation. The worker constructs and initialises
the service but nothing calls assessAfterFailure yet, so behaviour is unchanged.

🔧

server/src/api/validation/settingsValidation.ts

@@ -1,6 +1,15 @@
 import { CHECK_TTL_SENTINEL } from "@/domain/checks/check.type.js";
+import { MAX_EGRESS_POLL_INTERVAL_SECONDS, MAX_EGRESS_TARGETS, MIN_EGRESS_POLL_INTERVAL_SECONDS } from "@/domain/egress/egress.type.js";
 import { z } from "zod";
 
+// A reliability target is a bare host/IP (ICMP ping), host:port (TCP connect) or an http(s) URL.
+const egressTargetValidation = z
+	.string()
+	.trim()
+	.min(1)
+	.max(253)
+	.regex(/^(https?:\/\/\S+|[A-Za-z0-9.\-:[\]]+)$/, "Invalid egress target");
+
 //****************************************
 // Settings Validations
 //****************************************
@@ -42,6 +51,11 @@ export const updateAppSettingsBodyValidation = z
 			.optional(),
 		globalProxyEnabled: z.boolean().optional(),
 		globalProxyId: z.string().nullable().optional(),
+
+		egressCheckEnabled: z.boolean().optional(),
+		egressCheckTargets: z.array(egressTargetValidation).max(MAX_EGRESS_TARGETS).optional(), // empty list falls back to DEFAULT_EGRESS_TARGETS
+		egressPollIntervalSeconds: z.number().int().min(MIN_EGRESS_POLL_INTERVAL_SECONDS).max(MAX_EGRESS_POLL_INTERVAL_SECONDS).optional(),
+		egressNotifications: z.array(z.string().regex(/^[a-f\d]{24}$/i, "Invalid notification id")).optional(),
 	})
 	.strip()
 	.superRefine((body, ctx) => {