Add generative garden audio

src/audio/samples/README.md

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+Piano samples are Salamander Grand Piano V3 samples by Alexander Holm,
+transcoded from OGG Vorbis to AAC M4A for iOS browser playback and distributed
+under CC BY 3.0.
+
+Source package: @audio-samples/piano-velocity12
+Source recording: https://archive.org/details/SalamanderGrandPianoV3
+License: https://creativecommons.org/licenses/by/3.0/
+
+Checked-in subset: velocity layer `v12`, every minor-third anchor from A0
+through C8: A, C, Dsharp, and Fsharp for octaves 1-7, plus A0, A7, and C8.
+The app derives MIDI values from those note names in `piano-samples.ts`.
+
+Repro notes: start from the matching `v12` OGG files in the source package and
+transcode each selected sample to AAC/M4A without renaming the note/velocity
+stem. The expected output filenames are `<note>v12.m4a`, for example
+`C4v12.m4a`.