BBP2MIDI V13 CHANGELOG

V13.0
- Retains the V12/V11 musical decoding core unchanged for regression safety.
- Separates BBP decoding success from MIDI destination write success.
- Writes through a temporary MIDI and atomically replaces the destination where possible.
- If the destination MIDI is locked, preserves the newly converted MIDI as a unique "(converted)" file instead of reporting a false conversion failure.
- Adds clearer exception type to batch failure messages.
- External edge corpus: 3 new BBPs were exercised; all 3 decoded successfully, and their supplied MIDIs match fresh output byte-for-byte.

