feat(credits): solde IA unique (option M), packs Stripe et polish billing

Un pot de crédits global (BASIC 100 / PRO 1 000 / BUSINESS 4 000) remplace
les seaux par fonction côté débit. Packs one-shot S/M/L, admin sans seaux
legacy, usage multi-features, hints de coût, anti-flash thème et hydratation
admin. Inclut aussi le pipeline slides renforcé et la page publique polishée.

memento-note/app/api/usage/current/route.ts

@@ -1,27 +1,48 @@
-import { NextResponse } from 'next/server';
-import { auth } from '@/auth';
-import { getUserQuotas, getEffectiveTier } from '@/lib/entitlements';
+import { NextResponse } from 'next/server'
+import { auth } from '@/auth'
+import { getCreditUsageSummary, getQuotasCompatFromCredits } from '@/lib/credits'
 
-export const dynamic = 'force-dynamic';
+export const dynamic = 'force-dynamic'
 
 export async function GET() {
-  const session = await auth();
+  const session = await auth()
 
   if (!session?.user?.id) {
-    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
   }
 
   try {
-    const [quotas, tier] = await Promise.all([
-      getUserQuotas(session.user.id),
-      getEffectiveTier(session.user.id),
-    ]);
-    return NextResponse.json({ quotas, tier });
+    const summary = await getCreditUsageSummary(session.user.id)
+    // Compat anciens clients : quotas dérivés des crédits
+    const quotas = await getQuotasCompatFromCredits(session.user.id)
+
+    return NextResponse.json({
+      tier: summary.tier,
+      period: summary.period,
+      balance: {
+        totalRemaining: summary.balance.unlimited
+          ? null
+          : summary.balance.totalRemaining,
+        subscriptionRemaining: summary.balance.unlimited
+          ? null
+          : summary.balance.subscriptionRemaining,
+        purchasedRemaining: summary.balance.purchasedRemaining,
+        subscriptionGranted: summary.balance.unlimited
+          ? null
+          : summary.balance.subscriptionGranted,
+        subscriptionSpent: summary.balance.subscriptionSpent,
+        spentThisPeriod: summary.balance.spentThisPeriod,
+        unlimited: summary.balance.unlimited,
+      },
+      breakdown: summary.breakdown,
+      // legacy
+      quotas,
+    })
   } catch (error) {
-    console.error('[usage/current] Failed to fetch quotas:', error);
+    console.error('[usage/current] Failed to fetch usage data:', error)
     return NextResponse.json(
       { error: 'Failed to fetch usage data' },
       { status: 503 },
-    );
+    )
   }
 }