fix(send_message): deliver Matrix media via adapter

Matrix media delivery was silently dropped by send_message because Matrix
wasn't wired into the native adapter-backed media path. Only Telegram,
Discord, and Weixin had native media support.

Adds _send_matrix_via_adapter() which creates a MatrixAdapter instance,
connects, sends text + media via the adapter's native upload methods
(send_document, send_image_file, send_video, send_voice), then disconnects.

Also fixes a stale URL-encoding assertion in test_send_message_missing_platforms
that broke after PR #10151 added quote() to room IDs.

Cherry-picked from PR #10486 by helix4u.

tests/tools/test_send_message_missing_platforms.py

@@ -123,7 +123,7 @@ class TestSendMatrix:
         session.put.assert_called_once()
         call_kwargs = session.put.call_args
         url = call_kwargs[0][0]
-        assert url.startswith("https://matrix.example.com/_matrix/client/v3/rooms/!room:example.com/send/m.room.message/")
+        assert url.startswith("https://matrix.example.com/_matrix/client/v3/rooms/%21room%3Aexample.com/send/m.room.message/")
         assert call_kwargs[1]["headers"]["Authorization"] == "Bearer syt_tok"
         payload = call_kwargs[1]["json"]
         assert payload["msgtype"] == "m.text"