feat(alerts): add container health alerts with log excerpt on notifications (#2225)

Add a new "ContainerHealth" alert type that fires when a Docker container's
health check reports unhealthy, and resolves when it recovers. This mirrors
the existing Status (up/down) alert pattern: an alert can be armed per system
and honors the "min minutes" delay before firing.

When the alert fires, the notification (email and any configured webhook,
including Discord via shoutrrr) includes a log excerpt fetched live from the
agent for up to 2 of the unhealthy containers, prioritizing lines containing
"error" or "fatal" (falling back to the log tail if none match), capped to
keep the message well under Discord's size limit.

---------

Co-authored-by: hank <hank@henrygd.me>

internal/site/src/lib/alerts.ts

@@ -1,5 +1,5 @@
 import { t } from "@lingui/core/macro"
-import { CpuIcon, HardDriveIcon, MemoryStickIcon, ServerCrashIcon, ServerIcon } from "lucide-react"
+import { ContainerIcon, CpuIcon, HardDriveIcon, MemoryStickIcon, ServerCrashIcon, ServerIcon } from "lucide-react"
 import type { RecordSubscription } from "pocketbase"
 import { EthernetIcon, GpuIcon } from "@/components/ui/icons"
 import { $alerts } from "@/lib/stores"
@@ -104,6 +104,16 @@ export const alertInfo: Record<string, AlertInfo> = {
 		start: 20,
 		invert: true,
 	},
+	ContainerHealth: {
+		name: () => t`Container Health`,
+		unit: "",
+		icon: ContainerIcon,
+		desc: () => t`Triggers when a Docker container's health check reports unhealthy`,
+		note: () =>
+			t`Notifications may include recent container log excerpts.`,
+		/** "for x minutes" is appended to desc when only one value */
+		singleDesc: () => `${t`Container`} ${t`Unhealthy`}`,
+	},
 	SystemdFailed: {
 		name: () => t`Failed Services`,
 		unit: "",