feat(settings): replace single-spinner loading with skeleton rows on Thresholds and Sources

Replaces the centred `<Loader2 /> Loading` line in
`<ThresholdsEditorSection>` and `<SourcesSection>` with a skeleton
list whose row count matches the loaded UI (14 rows each — one per
`METRIC_ORDER` entry and one per `SOURCE_PRIORITY_METRIC_KEYS` entry
respectively). The skeleton rows reuse the live UI's container
classes (`border-border space-y-3 rounded-lg border p-4` on
Thresholds; `border-border bg-background/30 space-y-2 rounded-md
border p-3` on Sources) so the post-fetch swap lands in place. The
`<Skeleton>` primitive's `motion-reduce:animate-none` covers the
reduced-motion preference. Combined with the `min-h` shell reserve
from the previous commit, this removes the page-height jump that
landed under the sticky sidebar when these two sections finished
loading.

src/components/settings/sources-section.tsx

@@ -40,6 +40,7 @@ import {
 } from "lucide-react";
 
 import { Button } from "@/components/ui/button";
+import { Skeleton } from "@/components/ui/skeleton";
 import { useTranslations } from "@/lib/i18n/context";
 import { queryKeys } from "@/lib/query-keys";
 import {
@@ -314,10 +315,7 @@ export function SourcesSection() {
         </p>
 
         {isLoading || !priority ? (
-          <div className="text-muted-foreground flex items-center gap-2 text-sm">
-            <Loader2 className="h-4 w-4 animate-spin" />
-            {t("common.loading")}
-          </div>
+          <SourcesSkeletonList />
         ) : (
           <div className="space-y-3">
             {SOURCE_PRIORITY_METRIC_KEYS.map((metric) => {
@@ -564,3 +562,33 @@ export function SourcesSection() {
     </section>
   );
 }
+
+/**
+ * Skeleton placeholder rendered while `/api/auth/me/source-priority`
+ * is in flight. Reserves one row per `SOURCE_PRIORITY_METRIC_KEYS`
+ * entry at roughly the loaded height so the page does not jump when
+ * the fetched ladder list swaps in. The pulsing animation honours
+ * `prefers-reduced-motion` via Tailwind's `motion-reduce:animate-none`.
+ */
+function SourcesSkeletonList() {
+  return (
+    <div
+      className="space-y-3"
+      data-testid="sources-skeleton"
+      aria-hidden="true"
+    >
+      {SOURCE_PRIORITY_METRIC_KEYS.map((metric) => (
+        <div
+          key={metric}
+          className="border-border bg-background/30 space-y-2 rounded-md border p-3"
+        >
+          <Skeleton className="h-4 w-40" />
+          <div className="space-y-1">
+            <Skeleton className="h-9 w-full rounded-md" />
+            <Skeleton className="h-9 w-full rounded-md" />
+          </div>
+        </div>
+      ))}
+    </div>
+  );
+}

src/components/settings/thresholds-editor-section.tsx

@@ -3,15 +3,11 @@
 import { useState } from "react";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { toast } from "sonner";
-import {
-  SlidersHorizontal,
-  RotateCcw,
-  Loader2,
-  AlertTriangle,
-} from "lucide-react";
+import { SlidersHorizontal, RotateCcw, AlertTriangle } from "lucide-react";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
+import { Skeleton } from "@/components/ui/skeleton";
 import { Switch } from "@/components/ui/switch";
 import { Badge } from "@/components/ui/badge";
 import { useTranslations, useFormatters } from "@/lib/i18n/context";
@@ -147,10 +143,7 @@ export function ThresholdsEditorSection({ id }: { id: string }) {
       </div>
 
       {isLoading || !data ? (
-        <div className="text-muted-foreground flex items-center gap-2 text-sm">
-          <Loader2 className="h-4 w-4 animate-spin" />
-          {t("common.loading")}
-        </div>
+        <ThresholdsSkeletonList />
       ) : (
         <div className="space-y-3">
           {METRIC_ORDER.map((metric) => (
@@ -170,6 +163,41 @@ export function ThresholdsEditorSection({ id }: { id: string }) {
   );
 }
 
+/**
+ * Skeleton placeholder rendered while `/api/user/thresholds` is in
+ * flight. Reserves one row per `METRIC_ORDER` entry at roughly the
+ * loaded height so the page does not jump when the fetched list
+ * swaps in. The pulsing animation honours `prefers-reduced-motion`
+ * via Tailwind's `motion-reduce:animate-none`.
+ */
+function ThresholdsSkeletonList() {
+  return (
+    <div
+      className="space-y-3"
+      data-testid="thresholds-skeleton"
+      aria-hidden="true"
+    >
+      {METRIC_ORDER.map((metric) => (
+        <div
+          key={metric}
+          className="border-border space-y-3 rounded-lg border p-4"
+        >
+          <div className="flex items-center justify-between gap-3">
+            <div className="min-w-0 space-y-2">
+              <Skeleton className="h-4 w-32" />
+              <Skeleton className="h-3 w-48" />
+            </div>
+            <div className="flex shrink-0 items-center gap-2">
+              <Skeleton className="h-3 w-12" />
+              <Skeleton className="h-5 w-9 rounded-full" />
+            </div>
+          </div>
+        </div>
+      ))}
+    </div>
+  );
+}
+
 interface MetricRowProps {
   metric: ThresholdMetric;
   effective: EffectiveRange | undefined;