Fix inconsistent SVG tile icon sizes

SVG icons with explicit width/height attributes rendered tiny because
max-width/max-height only caps intrinsic size and never scales up, while
dimensionless SVGs defaulted large and were capped to 60px. Pin .app-icon
to a fixed 60x60 box with object-fit: contain so every icon renders at a
consistent size while preserving aspect ratio.

Fixes #1582

public/css/app.css

@@ -927,9 +927,10 @@ div.create .input input, div.create .input select {
 }
 
 .app-icon {
-  max-width: 60px;
+  width: 60px;
+  height: 60px;
+  object-fit: contain;
   display: block;
-  max-height: 60px;
 }
 
 .sidenav {

resources/assets/sass/_app.scss

@@ -722,9 +722,10 @@ div.create {
 	flex: 0 0 60px;
 }
 .app-icon {
-	max-width: 60px;
+	width: 60px;
+	height: 60px;
+	object-fit: contain;
 	display: block;
-	max-height: 60px;
 }
 
 .sidenav {