feat: move tailscale device discovery and settings into a plugin

Adds plugins/tailscale/ with a devices sidebar tab, admin settings
section, and re-auth dialog. Host Metrics tailscale manager card and
SSH re-auth banner parsing stay in core.

src/ui/ssh/dialogs/TailscaleCheckDialog.tsx

@@ -1,89 +0,0 @@
-import React from "react";
-import { Button } from "@/components/button.tsx";
-import { Shield, ExternalLink, Loader2 } from "lucide-react";
-import { useTranslation } from "react-i18next";
-
-interface TailscaleCheckDialogProps {
-  isOpen: boolean;
-  authUrl: string;
-  message?: string;
-  stage: "prompt" | "waiting";
-  onCancel: () => void;
-  onOpenUrl: () => void;
-  backgroundColor?: string;
-}
-
-export function TailscaleCheckDialog({
-  isOpen,
-  authUrl,
-  message,
-  stage,
-  onCancel,
-  onOpenUrl,
-  backgroundColor,
-}: TailscaleCheckDialogProps) {
-  const { t } = useTranslation();
-
-  if (!isOpen) return null;
-
-  return (
-    <div className="absolute inset-0 flex items-center justify-center z-500 animate-in fade-in duration-200">
-      <div
-        className="absolute inset-0 bg-canvas rounded-md"
-        style={{ backgroundColor: backgroundColor || undefined }}
-      />
-      <div className="bg-card border border-border w-full max-w-md mx-4 relative z-10 animate-in fade-in zoom-in-95 duration-200">
-        <div className="p-4 border-b border-border">
-          <div className="flex items-center gap-2">
-            <Shield className="size-4 text-accent-brand" />
-            <h3 className="text-xs font-bold uppercase tracking-widest">
-              {t("terminal.tailscaleCheckRequired")}
-            </h3>
-          </div>
-          <p className="text-[10px] font-bold uppercase tracking-tight text-muted-foreground mt-1">
-            {t("terminal.tailscaleCheckDescription")}
-          </p>
-        </div>
-        <div className="p-4 flex flex-col gap-4">
-          {message && (
-            <p className="text-xs text-muted-foreground whitespace-pre-wrap break-words">
-              {message}
-            </p>
-          )}
-
-          {stage === "prompt" && authUrl && (
-            <Button
-              type="button"
-              variant="outline"
-              onClick={onOpenUrl}
-              className="border-accent-brand/40 text-accent-brand hover:bg-accent-brand/10 rounded-none text-[10px] font-bold uppercase tracking-widest w-full flex items-center gap-2"
-            >
-              <ExternalLink className="size-3.5" />
-              {t("terminal.tailscaleCheckOpenBrowser")}
-            </Button>
-          )}
-
-          {stage === "waiting" && (
-            <div className="flex items-center gap-3 py-2">
-              <Loader2 className="size-4 animate-spin text-accent-brand shrink-0" />
-              <p className="text-xs text-muted-foreground">
-                {t("terminal.tailscaleCheckWaiting")}
-              </p>
-            </div>
-          )}
-
-          <div className="flex justify-end">
-            <Button
-              type="button"
-              variant="ghost"
-              onClick={onCancel}
-              className="rounded-none text-[10px] font-bold uppercase tracking-widest"
-            >
-              {t("common.cancel")}
-            </Button>
-          </div>
-        </div>
-      </div>
-    </div>
-  );
-}