最后一架钢琴

Create a single self-contained index.html: a ~2-minute animated short called "the last piano", in a hand-drawn crayon and watercolor style.

Scene: a small rusty robot with one glowing eye walks through a dark, empty city in the rain and finds an old upright piano under a broken streetlamp. Later a black cat shows up to listen.

Music: compose an original piano piece (Am - F - C - G) and synthesize it in Web Audio. It starts with one unsure note and grows into full chords.

Sync: one timeline drives both. The robot's hands hit the keys that are actually sounding. Every note turns on a window in the city, the rain turns to snow, and the final chord lights up everything that's left.

Rules: Canvas 2D only, no libraries, no external assets.