What was the first official BTC miner software? I know that the first and official wallet is bitcoin-qt. This wallet has code here: https://github.com/bitcoin/bitcoin

What was the first official miner software? I understand that bitcoin-qt never use as miner software. Where is official code of miner software?
The first official mining software was Bitcoin Core (then known simply as Bitcoin, later bitcoin-qt), and it still serves as a reference mining implementation, making it the "official" miner. See its miner.cpp file, for example.

Bitcoin Core uses your CPU to mine. Mining eventually moved to GPUs and ASICs, so that mining on a CPU is practically pointless right now. In that sense, you should never use Bitcoin Core as mining software. But it still is mining software.