ffi #jni_main slice 2: AOT pipeline — .java + javac + d8 → classes.dex in APK

Compilation.lowering_jni_main_decls is populated by lowerToIR (iterating
foreign_class_map for is_main && !is_foreign && runtime==jni_class,
deduped by foreign_path); each entry carries the pre-rendered Java source
from jni_java_emit.emitJavaSource.

createApk extended: when the emission list is non-empty, write each
.java under <stage>/java/<pkg>/<Class>.java, javac --release 11 to
<stage>/classes/, d8 --release --lib <android_jar> --output <stage>
to produce <stage>/classes.dex, then zip the .dex into the unaligned
APK at root level. javac discovery: $JAVA_HOME/bin/javac first, then
`which javac`.

Manifest still hardcodes android.app.NativeActivity (slice 3 wires the
user's class name + android:hasCode="true"), so the bundled .dex is
present but unreferenced at runtime. End-to-end verified via dexdump on
the smoke example's APK — Lco/swipelab/sxjnimain/SxApp; extending
NativeActivity shows up in classes.dex. Non-#jni_main APK builds
(99-android-egl-clear.sx) produce the same shape as before.

Cross-compile tuple added for examples/ffi-jni-main-01-emit.sx
(compile-only — APK exercise is manual).

src/main.zig

@@ -612,7 +612,7 @@ fn compileWithTimer(allocator: std.mem.Allocator, io: std.Io, input_path: []cons
     // Wrap into an .apk if requested (Android).
     if (merged_config.apk_path) |ap| {
         timer.mark();
-        sx.target.createApk(allocator, io, final_output, merged_config) catch std.process.exit(1);
+        sx.target.createApk(allocator, io, final_output, merged_config, comp.getJniMainEmissions()) catch std.process.exit(1);
         timer.record("apk");
         std.debug.print("apk: {s}\n", .{ap});
     }