Route MIDI notes by channel; punch-in from MIDI on the Tracker tab (v0.20.0)

Incoming USB/BLE MIDI notes were dropping their channel and always playing the
generic default-synth pool, ignoring the mixer routing. Now the parser keeps the
channel nibble (exposed 1-based, 1..16) on InputAction.NoteOn/NoteOff, and the
ViewModel routes a channelled note through engine.busNoteOn/busNoteOff — sounding
the mixer track(s) whose midiChannel matches, through their instrument and full
insert chain, exactly like the on-screen keyboard. Channel-less sources (physical
keyboard) keep the previous audition path.

On the Tracker tab with punch-in armed, a MIDI note now also punches into the
focused cell, recording its own velocity and channel and advancing by the skip
step (punchNote gained velocity/channel parameters). Off the tracker tab or with
punch-in off, MIDI only auditions.

Note: routing is strict, so a note is audible only on a track whose MIDI channel
matches and that has an instrument assigned (new projects start with buses on the
empty channel 0).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/build.gradle.kts

@@ -22,8 +22,8 @@ android {
         // (android.media.midi) and AAudio low-latency audio we rely on.
         minSdk = 26
         targetSdk = 34
-        versionCode = 45
-        versionName = "0.19.0"
+        versionCode = 46
+        versionName = "0.20.0"
 
         // We provide our own instrumentation runner if/when tests are added.
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"