Add per-channel VU meters inside the mixer faders (v0.9.0)

The render loop now tracks each bus's post-fader/post-FX peak per block and folds
it into a decaying meter value (instant attack, ~300 ms release) plus a clip
latch (~0.8 s when the bus crosses 0 dBFS). Exposed via channelMeter /
channelClipped and surfaced on the ViewModel.

Each mixer fader paints, in one drawBehind, a VU meter inside its volume fill:
rising from the bottom, coloured green -> amber by absolute level with a red tip,
and solid red while the bus clips. A per-frame ticker writes into stable state
objects read only in the fader's draw phase, so meter movement repaints just the
four faders (no recomposition); an unchanged write is a no-op, so a silent mixer
costs nothing but the frame tick.

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 = 24
-        versionName = "0.8.1"
+        versionCode = 25
+        versionName = "0.9.0"
 
         // We provide our own instrumentation runner if/when tests are added.
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"