polish(app): skeleton loaders for Compare and the Audit lens

The motion batch gave five sections shimmer skeletons on first load but
missed Compare and Models' Audit lens (both still showed bare loading
text in an empty panel). Same SectionSkeleton treatment now.

250/250.

app/renderer/sections/Compare.tsx

@@ -4,6 +4,7 @@ import { CliErrorPanel } from '../components/CliErrorPanel'
 import { Dropdown } from '../components/Dropdown'
 import { EmptyNote } from '../components/EmptyState'
 import { Panel } from '../components/Panel'
+import { SectionSkeleton } from '../components/Skeleton'
 import { usePolled } from '../hooks/usePolled'
 import { formatCompact, formatUsd } from '../lib/format'
 import { codeburn } from '../lib/ipc'
@@ -60,11 +61,7 @@ export function Compare({
 
   if (!models.data) {
     if (models.error) return <CliErrorPanel error={models.error} subject="model comparisons" />
-    return (
-      <Panel title="Compare">
-        <EmptyNote>Scanning model usage…</EmptyNote>
-      </Panel>
-    )
+    return <SectionSkeleton label="Scanning model usage…" rows={4} />
   }
 
   if (models.data.length < 2) {
@@ -144,11 +141,7 @@ function CompareReport({
 
   if (!report.data) {
     if (report.error) return <CliErrorPanel error={report.error} subject="model comparisons" />
-    return (
-      <Panel title="Compare">
-        <EmptyNote>Comparing models…</EmptyNote>
-      </Panel>
-    )
+    return <SectionSkeleton label="Comparing models…" rows={4} />
   }
 
   const performance = report.data.metrics.filter(metric => metric.section === 'Performance')

app/renderer/sections/Models.tsx

@@ -133,11 +133,7 @@ function AuditLens({
 
   if (!report.data) {
     if (report.error) return <CliErrorPanel error={report.error} subject="the token audit" />
-    return (
-      <Panel title="Audit">
-        <EmptyNote>Auditing token usage…</EmptyNote>
-      </Panel>
-    )
+    return <SectionSkeleton label="Auditing token usage…" rows={5} />
   }
 
   return (