When was the first piano built/marketed/sold whose pedals were mounted on what we now call a lyre, instead of onto a harpsichord-like crossbar between the front legs?
The short answer is that it depends on whom you ask. This wikipedia article is a very interesting read on the subject of piano pedals and their history. Here's a quote of the material most relevant to your question:
Americus Backers' 1772 grand, his only surviving instrument, has what are believed to be original pedals, and is most likely the first piano to use pedals rather than knee levers. A square piano built by Adam Beyer of London in 1777 has a damper pedal, as do pianos built by John Broadwood, ca. 1783.
So, somewhere in the late 18th century.