Self-service key check — added 31.08.2026.

Why it exists: a customer with a perfectly valid key could not tell whether the problem was the key, the subscription or the header, and had to open a support ticket to find out. This answers all three in one call.

Deliberately NOT premium-gated: it must answer WITHOUT a key too, otherwise the diagnostic returns the same 401 it is meant to explain. Never returns the key itself — prefix only.