Validates a 5-digit Turkish postal code and resolves the province from the first two digits (plate map).

PTT postal codes are five digits; the leading pair matches the province plate code for the 81 provinces. This endpoint checks the shape, maps 01–81 to the province name, and returns null with confidence none when the prefix is outside that range — it does not invent a district. District-level resolution needs the full PTT directory and is out of scope here.

Credits per call: 1 · Operation id: tr_posta_kodu