Add key signature properties

[errows]

Adds support for root_note and scale_name properties to enable key signature control via OSC.

Changes

• Added root_note to properties_rw (enables /live/song/get/root_note and /live/song/set/root_note)
• Added scale_name to properties_rw (enables /live/song/get/scale_name and /live/song/set/scale_name)

Usage

/live/song/get/root_note     # Returns 0-11 (C=0, C#=1, etc.)
/live/song/set/root_note 9   # Sets to A
/live/song/get/scale_name    # Returns "Minor", "Major", etc.
/live/song/set/scale_name Minor

Uses standard AbletonOSC property handling - no custom handlers needed.