Share full projects as .szgz bundles between instances (v0.16.0)

Add Export/Import project buttons to Settings → Project. A bundle is a ZIP holding
the full .szg project plus every sample WAV it references (Sampler pads, SoundFont),
so unlike a plain .szg — whose sample ids only resolve on the originating device —
it opens complete on another Sizzletracker instance.

Export shares the bundle via the system share sheet. Import replaces the current
project, extracts the WAVs to a persistent content-addressed samples dir, re-points
each slot's padNFile/sfFile at the extracted file, then rehydrates — so the audio is
restored for the session and survives a restart. Invalid files are rejected cleanly.
Covered by ProjectBundleIoTest.

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 = 40
-        versionName = "0.15.1"
+        versionCode = 41
+        versionName = "0.16.0"
 
         // We provide our own instrumentation runner if/when tests are added.
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"