fix: notepat hold uses F11 (pickup)/F10 (hangup), install copy debug
- F11 (green pickup phone key): engage hold/latch
- F10 (red hangup phone key): clear hold, stop held notes
- F12: metronome (moved from F10)
- F8 hold removed (replaced by phone keys)
- Fixed obx const reassignment crash in HOLD indicator (use hbx)
- Added detailed errno logging to copy_file for install diagnosis
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>