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/src/main/AndroidManifest.xml

@@ -0,0 +1,66 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools">
+
+    <!-- ===== Permissions =====
+         RECORD_AUDIO       : ad-hoc sample recorder (mic / USB audio in).
+         FOREGROUND_SERVICE : keep the sequencer alive while the app is backgrounded.
+         FOREGROUND_SERVICE_MEDIA_PLAYBACK : Android 14 requires a typed FGS.
+         POST_NOTIFICATIONS : show the media transport notification (Android 13+).
+         BLUETOOTH_CONNECT  : Bluetooth MIDI + gamepad on Android 12+. -->
+    <uses-permission android:name="android.permission.RECORD_AUDIO" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_MEDIA_PLAYBACK" />
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
+    <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
+
+    <!-- Hardware we can *use* but do not *require* (so the app still installs on
+         devices without them). Code must always feature-detect at runtime. -->
+    <uses-feature android:name="android.hardware.usb.host" android:required="false" />
+    <uses-feature android:name="android.software.midi" android:required="false" />
+    <uses-feature android:name="android.hardware.gamepad" android:required="false" />
+    <uses-feature android:name="android.hardware.bluetooth" android:required="false" />
+    <uses-feature android:name="android.hardware.microphone" android:required="false" />
+
+    <application
+        android:name=".SizzleApp"
+        android:allowBackup="true"
+        android:icon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:supportsRtl="false"
+        android:theme="@style/Theme.Sizzletracker">
+
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:configChanges="orientation|screenSize|keyboardHidden|navigation|keyboard"
+            android:launchMode="singleTop"
+            android:theme="@style/Theme.Sizzletracker">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+
+            <!-- Announce that we can be a USB-MIDI aware app; the system routes
+                 attach events here so we can auto-connect controllers. -->
+            <intent-filter>
+                <action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" />
+            </intent-filter>
+            <meta-data
+                android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED"
+                android:resource="@xml/usb_device_filter" />
+        </activity>
+
+        <!-- Foreground service that owns the audio engine so playback survives
+             when the UI is not visible, and drives the media notification. -->
+        <service
+            android:name=".playback.PlaybackService"
+            android:exported="true"
+            android:foregroundServiceType="mediaPlayback">
+            <intent-filter>
+                <action android:name="androidx.media3.session.MediaSessionService" />
+            </intent-filter>
+        </service>
+
+    </application>
+</manifest>