Returns the top N most frequently used keys by usage count:

• Key identification and algorithm
• Usage count and limits
• Usage percentage of max limit

totalUsageCount covers the WHOLE inventory in scope, not only the limit keys listed, and
is served with the usageWindow it is measured over (ALL_TIME) plus the i18n key naming it.
The health-summary endpoint publishes a figure under the same label; both now state their own
span, so a reader can tell whether they are comparing two measurements or reading one twice.

Use this for capacity planning and identifying critical dependencies.

Authorization:
• Tenant admins: view own tenant's analytics only
• Platform admins: view any tenant's analytics

Path Parameter Validation:
The tenantId in the URL must match the JWT tenantId claim
(unless authenticated as platform admin with PLATFORM.ROOT scope).