hardcode padding in order to make PopupMenuButton actually .narrow

This is needed because of a flutter bug, see https://github.com/flutter/flutter/issues/193656.

flake.lock

@@ -89,11 +89,11 @@
     },
     "nixpkgs_2": {
       "locked": {
-        "lastModified": 1790185690,
+        "lastModified": 1790689126,
-        "narHash": "sha256-xJ+X4hBtOcAFGBOe5nAMyMUeF9foJBmIOu3NjBqBycU=",
+        "narHash": "sha256-ilerN1WLSvF+HMjziC/Wv99J5y02maDH+6hZPwsORKg=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "4975466d324710c576dc11ad614684e6bd8cad8e",
+        "rev": "b4fd65b198c599cbe814fcb9f42d25d021595ec9",
         "type": "github"
       },
       "original": {

lib/widgets/composer/composer.dart

@@ -141,8 +141,11 @@ class const Composer(
                               icon: Icon(Icons.emoji_emotions),
                             ),
                             PopupMenuButton(
-                              style: .new(iconButtonWidth: .narrow),
                               tooltip: "Add media",
+
+                              // `style` has no effect due to https://github.com/flutter/flutter/issues/193656, so `padding` is set from material_ui/lib/src/generated/icon_button_defaults_m3e.g.dart manually.
+                              padding: .fromSTEB(4.0, 6.0, 4.0, 6.0),
+                              style: .new(iconButtonWidth: .narrow),
                               enabled: attachment == null,
                               itemBuilder: (context) => [
                                 if (Platform.isAndroid || Platform.isIOS)