fix(icons): render MaterialSymbol Icons that rely on defaultMinSize

The Canvas-based MaterialSymbol Icon collapsed to 0x0 whenever callers
didn't pass an explicit size modifier (e.g. ArrowBackIcon, ClearTextIcon).

Canvas is a Spacer + drawBehind, and Spacer's measure policy only uses
maxWidth/maxHeight when the incoming constraints are fixed. Inside an
IconButton (state layer 40dp, content constraints 0..40), defaultMinSize
only lifts minWidth/minHeight, leaving the constraints unfixed - so
Spacer picked 0x0 and the glyph never drew. Icons that passed
Modifier.size(N.dp) worked only because size(...) produces fixed
constraints.

Swap Canvas for an empty Box with drawBehind. Box's EmptyBoxMeasurePolicy
uses minWidth/minHeight, so defaultMinSize(24, 24) now takes effect when
no size modifier is supplied - matching Material3's own Icon behavior.

https://claude.ai/code/session_01V9esGUFH72ujCQNWCAnjKN

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/icons/symbols/Icon.kt

@@ -20,11 +20,12 @@
  */
 package com.vitorpamplona.amethyst.commons.icons.symbols
 
-import androidx.compose.foundation.Canvas
+import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.defaultMinSize
 import androidx.compose.material3.LocalContentColor
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.drawBehind
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.drawscope.scale
@@ -66,32 +67,32 @@ fun Icon(
             Modifier
         }
 
-    Canvas(
+    Box(
         modifier =
             modifier
                 .defaultMinSize(IconDefaultSize, IconDefaultSize)
-                .then(semanticsModifier),
-    ) {
-        val sizePx = size.minDimension
-        val fontSize = with(density) { sizePx.toSp() }
-        val layout =
-            textMeasurer.measure(
-                text = symbol.glyph,
-                style =
-                    TextStyle(
-                        fontFamily = fontFamily,
-                        fontSize = fontSize,
-                        color = tint,
-                    ),
-            )
-        val tx = (size.width - layout.size.width) / 2f
-        val ty = (size.height - layout.size.height) / 2f
-        if (mirror) {
-            scale(scaleX = -1f, scaleY = 1f, pivot = Offset(size.width / 2f, size.height / 2f)) {
-                translate(tx, ty) { drawText(layout) }
-            }
-        } else {
-            translate(tx, ty) { drawText(layout) }
-        }
-    }
+                .drawBehind {
+                    val sizePx = size.minDimension
+                    val fontSize = with(density) { sizePx.toSp() }
+                    val layout =
+                        textMeasurer.measure(
+                            text = symbol.glyph,
+                            style =
+                                TextStyle(
+                                    fontFamily = fontFamily,
+                                    fontSize = fontSize,
+                                    color = tint,
+                                ),
+                        )
+                    val tx = (size.width - layout.size.width) / 2f
+                    val ty = (size.height - layout.size.height) / 2f
+                    if (mirror) {
+                        scale(scaleX = -1f, scaleY = 1f, pivot = Offset(size.width / 2f, size.height / 2f)) {
+                            translate(tx, ty) { drawText(layout) }
+                        }
+                    } else {
+                        translate(tx, ty) { drawText(layout) }
+                    }
+                }.then(semanticsModifier),
+    )
 }