Initial commit: Sizzletracker Android music tracker

A retro, grid-based music tracker for Android (Kotlin + Jetpack Compose,
single Activity) with four equally-capable input methods (touch, keyboard,
gamepad, MIDI) and four tabs: tracker, mixer, toolbox, settings.

Highlights:
- Tracker: Canvas-drawn 4-track pattern grid over an 8-lane arrangement roll,
  with a glyph cache and draw-phase state reads so the playhead and edits
  redraw without per-frame recomposition.
- Audio: sample-accurate sequencer feeding a shared AudioEngine, driven by
  either a Kotlin AudioTrack loop or native Oboe/AAudio via JNI (16 KB-aligned
  native libs). media3 MediaSession for lock-screen/headset transport.
- Toolbox: 16 instrument/effect slots with a 2-octave audition keyboard;
  single-tap select, double-tap edit, long-press clear.
- Note entry: long-press cell popups (piano keyboard / value steppers) plus
  keyboard/gamepad stepping that resumes from the last note/channel entered.
  Velocity capped at 0x7F, channel at 16.
- Selection/clipboard (cut/copy/paste/delete) and .sng import/export
  compatible with the reference desktop tool.
- A `profile` build type (non-debuggable, debug-signed) for realistic
  on-device performance testing.
- Developer handover documentation under docs/.

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

app/build.gradle.kts

@@ -0,0 +1,121 @@
+// Build configuration for the single application module. This is where we turn
+// on Compose, set the min/target Android versions, and list dependencies.
+
+plugins {
+    alias(libs.plugins.android.application)
+    alias(libs.plugins.kotlin.android)
+    alias(libs.plugins.kotlin.compose)
+}
+
+android {
+    namespace = "com.reactorcoremeltdown.sizzletracker"
+    compileSdk = 34
+
+    // Native (Oboe) low-latency output backend; see src/main/cpp.
+    // NDK r27+ builds native libs 16 KB-page-aligned by default and ships a
+    // 16 KB-aligned libc++_shared.so (required for Android 15 / Google Play).
+    ndkVersion = "27.2.12479018"
+
+    defaultConfig {
+        applicationId = "com.reactorcoremeltdown.sizzletracker"
+        // minSdk 26 (Android 8.0) is the floor for the native MIDI API
+        // (android.media.midi) and AAudio low-latency audio we rely on.
+        minSdk = 26
+        targetSdk = 34
+        versionCode = 1
+        versionName = "0.1.0"
+
+        // We provide our own instrumentation runner if/when tests are added.
+        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+
+        externalNativeBuild {
+            cmake { arguments += "-DANDROID_STL=c++_shared" }
+        }
+    }
+
+    externalNativeBuild {
+        cmake {
+            path = file("src/main/cpp/CMakeLists.txt")
+            version = "3.22.1"
+        }
+    }
+
+    buildTypes {
+        release {
+            // Shrinking is off by default so newcomers get readable stack traces.
+            // Flip to true once the app stabilises.
+            isMinifyEnabled = false
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro",
+            )
+        }
+
+        // A realistic-performance variant for testing UI responsiveness on-device.
+        // The `debug` build is `debuggable = true`, which makes ART run the app
+        // un-optimised and makes Compose several times slower — so measuring UI
+        // "snappiness" on a debug build is misleading. This variant flips
+        // debuggability off (the single biggest perf lever) while reusing the debug
+        // signing key, so it still installs without a release keystore. R8/shrinking
+        // stays off to avoid needing JNI/Compose keep-rules for now.
+        create("profile") {
+            initWith(getByName("debug"))
+            isDebuggable = false
+            isJniDebuggable = false
+            signingConfig = signingConfigs.getByName("debug")
+            matchingFallbacks += "debug"
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+
+    kotlinOptions {
+        jvmTarget = "17"
+    }
+
+    buildFeatures {
+        compose = true
+        prefab = true // exposes the Oboe AAR's native headers/lib to CMake
+    }
+
+    packaging {
+        resources.excludes += "/META-INF/{AL2.0,LGPL2.1}"
+    }
+}
+
+dependencies {
+    implementation(libs.androidx.core.ktx)
+    implementation(libs.androidx.lifecycle.runtime.ktx)
+    implementation(libs.androidx.lifecycle.viewmodel.compose)
+    implementation(libs.androidx.activity.compose)
+
+    // Compose UI toolkit — the BOM keeps every Compose artifact on one version.
+    implementation(platform(libs.androidx.compose.bom))
+    implementation(libs.androidx.compose.ui)
+    implementation(libs.androidx.compose.ui.graphics)
+    implementation(libs.androidx.compose.ui.tooling.preview)
+    implementation(libs.androidx.compose.foundation)
+    implementation(libs.androidx.compose.material3)
+    implementation(libs.androidx.compose.material.icons.extended)
+    debugImplementation(libs.androidx.compose.ui.tooling)
+
+    // Background playback + media-style notification transport controls.
+    implementation(libs.androidx.media3.session)
+    implementation(libs.androidx.media3.common)
+
+    // Persistence for settings & themes.
+    implementation(libs.androidx.datastore.preferences)
+
+    // Coroutines for the audio/sequencer background work.
+    implementation(libs.kotlinx.coroutines.android)
+
+    // Oboe: low-latency native audio (AAudio) — the native output backend.
+    // 1.9.3+ ships 16 KB-page-aligned .so files (required by Android 15 / Play).
+    implementation("com.google.oboe:oboe:1.10.0")
+
+    // JVM unit tests for the pure model/io logic (no device needed).
+    testImplementation("junit:junit:4.13.2")
+}