style(home): color the success-rate meter by rate

The home overview bar stayed brown down to 80%. Color it continuously from red through yellow to green so it follows the measured success rate.

src/pages/HomeDashboard.css

@@ -283,7 +283,7 @@
 .home-stat-card h3 { margin: 0; color: var(--text-secondary); font-size: 12px; font-weight: 500; line-height: 1.5; }
 .home-stat-value { display: block; color: var(--text-primary); font-family: var(--font-mono); font-size: 28px; font-weight: 600; font-variant-numeric: tabular-nums; line-height: 1.15; letter-spacing: -.03em; }
 .home-stat-track { height: 5px; margin: 2px 0; overflow: hidden; border-radius: 3px; background: color-mix(in srgb, var(--stat-color) 13%, transparent); }
-.home-stat-track > span { display: block; height: 100%; border-radius: inherit; background: var(--stat-color); }
+.home-stat-track > span { display: block; height: 100%; border-radius: inherit; background: var(--stat-color); transition: width .25s ease, background-color .25s ease; }
 .home-stat-card p { margin: 0; color: var(--text-tertiary); font-size: 11px; line-height: 1.6; overflow-wrap: anywhere; }
 
 /* Use the desktop workspace height; smaller windows retain natural scrolling. */

src/pages/HomeOverviewCards.tsx

@@ -1,6 +1,7 @@
-import type { ReactNode } from 'react';
+import type { CSSProperties, ReactNode } from 'react';
 import { RefreshCw } from 'lucide-react';
 import { useI18n } from '../i18n';
+import { requestRateColor } from '../services/authFileRequests';
 import type { HomeOverviewSnapshot } from '../services/homeOverview';
 
 export function HomeOverviewCards({ snapshot, loading, coreReady, onRefresh, actions }: {
@@ -20,10 +21,11 @@ export function HomeOverviewCards({ snapshot, loading, coreReady, onRefresh, act
       id: 'usage', label: t('home.overview.successRate'),
       value: rate == null ? '—' : `${formatNumber(rate, { maximumFractionDigits: 1 })}%`,
       description: usage ? t(usage.totalRequests ? 'home.overview.requests' : 'home.overview.noRequests', { count: formatNumber(usage.totalRequests) }) : unavailable(false),
-      tone: rate == null ? 'neutral' : rate >= 95 ? 'success' : rate >= 80 ? 'warning' : 'error',
+      tone: 'neutral',
       error: snapshot?.errors.usage,
       percent: rate ?? null,
       meterLabel: t('home.overview.successRate'),
+      meterColor: rate == null ? undefined : requestRateColor(rate / 100),
     },
     {
       id: 'credentials', label: t('home.overview.credentials'),
@@ -56,7 +58,7 @@ export function HomeOverviewCards({ snapshot, loading, coreReady, onRefresh, act
         <div className="home-overview-actions">{actions}<button type="button" className="icon-button quiet" aria-label={t('home.overview.refresh')} title={t('home.overview.refresh')} disabled={loading} onClick={onRefresh}><RefreshCw size={14} className={loading ? 'spin' : undefined} /></button></div>
       </div>
       <div className="home-stat-grid">
-        {cards.map((card) => <article className={`home-stat-card ${card.tone}`} key={card.id} data-stat={card.id}>
+        {cards.map((card) => <article className={`home-stat-card ${card.tone}`} key={card.id} data-stat={card.id} style={'meterColor' in card && card.meterColor ? { '--stat-color': card.meterColor } as CSSProperties : undefined}>
           <h3>{card.label}</h3>
           <strong className="home-stat-value">{card.value}</strong>
           {'percent' in card && <div