fix(quotas): unifier le décompte IA (BYOK, rollback) et combler les fuites

Centralise la réserve via ai-quota, corrige admin unavailable (-1), brancher les routes sans quota et le host-pays brainstorm, avec usage-meter élargi, noms de clusters, MCP et ajustements dashboard/insights.

Co-authored-by: Cursor <cursoragent@cursor.com>

memento-note/tests/unit/plan-entitlements.test.ts

@@ -0,0 +1,19 @@
+import { describe, it, expect } from 'vitest';
+import {
+  ENTITLEMENT_UNAVAILABLE,
+  FALLBACK_TIER_LIMITS,
+} from '@/lib/plan-entitlements';
+
+describe('plan-entitlements unavailable sentinel', () => {
+  it('ENTITLEMENT_UNAVAILABLE should be -1', () => {
+    expect(ENTITLEMENT_UNAVAILABLE).toBe(-1);
+  });
+
+  it('fallback limits should not use unavailable sentinel', () => {
+    for (const tier of Object.keys(FALLBACK_TIER_LIMITS)) {
+      for (const [, limit] of Object.entries(FALLBACK_TIER_LIMITS[tier as keyof typeof FALLBACK_TIER_LIMITS])) {
+        expect(limit).not.toBe(ENTITLEMENT_UNAVAILABLE);
+      }
+    }
+  });
+});