add sheet music OCR CLI tool using Audiveris

Adds a Typer CLI (sheet-music-ocr) that converts scanned sheet music
(PDF, PNG, JPG, TIFF) to MusicXML via Audiveris, preserving lyrics and
text annotations. Includes Audiveris in the nix dev shell.

https://claude.ai/code/session_017GqUbuRDT58toRaxMtfRmf

shell.nix

@@ -14,6 +14,8 @@
       ssh-to-age
       gnupg
       age
+
+      audiveris
     ];
   };
 }