lib.App: Implement __aenter__() and __aexit__()

__aenter__() and __aexit__() are empty stubs. Using the application
as an async context manager therefore binds None in the as clause,
and releases nothing on exit: an AsyncRunner created through
call_async() keeps running in its thread, and since that thread is
not a daemon, the process does not exit after the block.

Return self from __aenter__(), and call close() from __aexit__(), so
that the context manager binds the application and releases all
resources on exit, whether the block exits normally or with an
exception.

Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.84.2
Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/App.py

@@ -222,8 +222,8 @@ class App:  # export
                     self.__eloop.close()
                 self.__eloop = None
 
-    async def __aenter__(self) -> None:
-        pass
+    async def __aenter__(self) -> App:
+        return self
 
     async def __aexit__(
         self,
@@ -231,7 +231,7 @@ class App:  # export
         exc: BaseException | None,
         tb: types.TracebackType | None,
     ) -> None:
-        pass
+        self.close()
 
     async def __run(self, argv: list[str] | None = None) -> None: