msglist: Clean up MessageImage layout

Adjust layout of MessageImage to match new design.
The transparent border mentioned was being treated
as external padding to the image, but it's actually
inner padding within the image, expanding the
image size to +2 on both axis.

Author: sirpengi

lib/widgets/content.dart

@@ -267,25 +267,24 @@ class MessageImage extends StatelessWidget {
         Navigator.of(context).push(getLightboxRoute(
           context: context, message: message, src: resolvedSrc));
       },
-      child: Align(
-        alignment: Alignment.centerLeft,
-        child: Padding(
-          // TODO clean up this padding by imitating web less precisely;
-          //   in particular, avoid adding loose whitespace at end of message.
-          // The corresponding element on web has a 5px two-sided margin…
-          // and then a 1px transparent border all around.
-          padding: const EdgeInsets.fromLTRB(1, 1, 6, 6),
-          child: Container(
-            height: 100,
-            width: 150,
-            alignment: Alignment.center,
-            color: const Color.fromRGBO(0, 0, 0, 0.03),
-            child: LightboxHero(
-              message: message,
-              src: resolvedSrc,
-              child: RealmContentNetworkImage(
-                resolvedSrc,
-                filterQuality: FilterQuality.medium))))));
+      child: Padding(
+        // TODO clean up this padding by imitating web less precisely;
+        //   in particular, avoid adding loose whitespace at end of message.
+        padding: const EdgeInsets.only(right: 5, bottom: 5),
+        child: ColoredBox(
+          color: const Color.fromRGBO(0, 0, 0, 0.03),
+          child: Padding(
+            padding: const EdgeInsets.all(1),
+            child: Center(
+              child: SizedBox(
+                height: 100,
+                width: 150,
+                child: LightboxHero(
+                  message: message,
+                  src: resolvedSrc,
+                  child: RealmContentNetworkImage(
+                    resolvedSrc,
+                    filterQuality: FilterQuality.medium))))))));
   }
 }