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.

plugins/tailscale/frontend/AdminTailscaleSection.tsx

@@ -0,0 +1,93 @@
+import type { Dispatch, SetStateAction } from "react";
+import { useTranslation } from "react-i18next";
+import { Button } from "@/components/button";
+import { Input } from "@/components/input";
+import { Network } from "lucide-react";
+import { AccordionSection } from "@/sidebar/AdminSettingsShared";
+
+// Was inline in AdminGeneralSettingsSection (src/ui/sidebar/AdminSettingsSections.tsx),
+// moved here into its own accordion section as part of the Tailscale plugin.
+// The backing routes (GET/PATCH /users/tailscale-settings) stay in core -
+// they are general user-settings infrastructure this plugin calls, not
+// something it owns.
+
+type AdminTailscaleSectionProps = {
+  open: boolean;
+  onToggle: () => void;
+  tailscaleApiKey: string;
+  setTailscaleApiKey: Dispatch<SetStateAction<string>>;
+  tailscaleApiBaseUrl: string;
+  setTailscaleApiBaseUrl: Dispatch<SetStateAction<string>>;
+  handleSaveTailscaleApiKey: () => void;
+};
+
+export function AdminTailscaleSection({
+  open,
+  onToggle,
+  tailscaleApiKey,
+  setTailscaleApiKey,
+  tailscaleApiBaseUrl,
+  setTailscaleApiBaseUrl,
+  handleSaveTailscaleApiKey,
+}: AdminTailscaleSectionProps) {
+  const { t } = useTranslation();
+
+  return (
+    <AccordionSection
+      label={t("admin.sectionTailscale")}
+      icon={<Network className="size-3.5" />}
+      open={open}
+      onToggle={onToggle}
+    >
+      <div className="flex flex-col gap-2 pt-2">
+        <div className="flex flex-col gap-0.5">
+          <span className="text-[10px] font-bold uppercase tracking-widest text-muted-foreground">
+            {t("admin.tailscaleApiKey")}
+          </span>
+          <span className="text-[10px] text-muted-foreground">
+            {t("admin.tailscaleApiKeyDescription")}{" "}
+            <a
+              href="https://docs.termix.site/features/networking/tailscale"
+              target="_blank"
+              rel="noreferrer"
+              className="text-accent-brand hover:underline"
+            >
+              {t("admin.tailscaleApiKeyDocsLink")}
+            </a>
+          </span>
+        </div>
+        <div className="flex items-center gap-2">
+          <Input
+            type="password"
+            value={tailscaleApiKey}
+            onChange={(e) => setTailscaleApiKey(e.target.value)}
+            placeholder="tskey-api-... / hskey-api-..."
+            className="text-sm"
+          />
+          <Button
+            variant="outline"
+            size="sm"
+            className="text-xs border-accent-brand/40 text-accent-brand hover:bg-accent-brand/10 hover:text-accent-brand h-7 shrink-0"
+            onClick={handleSaveTailscaleApiKey}
+          >
+            {t("common.save")}
+          </Button>
+        </div>
+        <div className="flex flex-col gap-1.5 mt-1">
+          <label className="text-[10px] font-semibold text-muted-foreground uppercase tracking-widest">
+            {t("admin.tailscaleApiBaseUrl")}
+          </label>
+          <span className="text-[10px] text-muted-foreground">
+            {t("admin.tailscaleApiBaseUrlDescription")}
+          </span>
+          <Input
+            value={tailscaleApiBaseUrl}
+            onChange={(e) => setTailscaleApiBaseUrl(e.target.value)}
+            placeholder="https://api.tailscale.com/api/v2"
+            className="text-sm"
+          />
+        </div>
+      </div>
+    </AccordionSection>
+  );
+}