ffi #jni_main: Alias.new(args) constructor dispatch via JNI NewObject

Adds the constructor-invocation arm of the foreign-class DSL:
`SurfaceView.new(ctx)` (where `SurfaceView` is a `#foreign #jni_class`
with `static new :: (ctx: *Context) -> *Self;`) lowers to
`FindClass(env, "android/view/SurfaceView") + GetMethodID(env, cls,
"<init>", "(args)V") + NewObject(env, cls, mid, args...)`. Returns
the fresh jobject.

  - inst.zig: `JniMsgSend.is_constructor` flag + `parent_class_path`
    re-purposed to carry the class being constructed (alongside its
    existing nonvirtual-super-class use). Mutually exclusive with
    `is_static` / `is_nonvirtual`.
  - lower.zig: `lowerCall.field_access` arm now recognises
    `Alias.method(args)` where `Alias` resolves in `foreign_class_map`
    and the matching member is `static`. `new` routes to a new
    `lowerForeignStaticCall` that derives a `(args)V` JNI descriptor
    and emits a `JniMsgSend` with `is_constructor=true`. Non-`new`
    static calls report a clear "use #jni_static_call" diagnostic
    until that sugar lands.
  - emit_llvm.zig: new `NewObject` vtable slot (28) + `emitJniConstructor`
    helper expanding the FindClass+GetMethodID+NewObject chain. The
    jni_msg_send arm short-circuits to it when `is_constructor` is set.

Smoke `ffi-jni-main-03-ctor.sx` exercises both this slice and the
previous super-dispatch slice in a single `onCreate` body: calls
`super.onCreate(b)` then constructs a `SurfaceView` with the Activity
as Context. IR shows the expected six-stage chain (FindClass+GetMethodID+
CallNonvirtual + FindClass+GetMethodID+NewObject); APK builds clean.

Naming caveat: the Java type `android.content.Context` clashes with
sx stdlib's `Context :: struct {...}` (heap-context). The smoke aliases
it `JContext` — future work could add a path-prefix or `as` rename
form on `#jni_class` to avoid the manual rename.

133 host / 6 cross / zig build test all green.

tests/cross_compile.sh

@@ -40,6 +40,9 @@ TUPLES=(
     # against the parent class (Activity by default). Compile-only check
     # — runtime correctness is verified by on-device chess deploy.
     "android|examples/ffi-jni-main-02-super.sx"
+    # `Alias.new(args)` constructor dispatch: lowers to FindClass +
+    # GetMethodID("<init>") + NewObject. Compile-only — runtime via chess.
+    "android|examples/ffi-jni-main-03-ctor.sx"
 )
 
 PASS=0

tests/expected/ffi-jni-main-03-ctor.exit

@@ -0,0 +1 @@
+0

tests/expected/ffi-jni-main-03-ctor.txt

@@ -0,0 +1 @@
+