feat(icons): swap drawer "Chess" menu icon to MaterialSymbols.ChessKnight

- Replace R.drawable.ic_chess (custom drawable) with MaterialSymbols.ChessKnight
  (U+F25E) in the navigation drawer's Chess menu entry. Knight is the most
  recognizable chess piece silhouette.
- Drop ic_chess.xml.

Chess board pieces (ChessPieceVectors.kt, CBurnett set) stay as ImageVector —
Material Symbols glyphs are monochrome and can't do the white-with-black-outline
style that keeps pieces visible on both light and dark squares.

https://claude.ai/code/session_016gV9gEaSud6kDMdcaqy8ti

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/drawer/DrawerContent.kt

@@ -548,8 +548,7 @@ fun ListContent(
             if (isDebug) {
                 NavigationRow(
                     title = R.string.route_chess,
-                    icon = R.drawable.ic_chess,
-                    iconReference = 1,
+                    icon = MaterialSymbols.ChessKnight,
                     tint = MaterialTheme.colorScheme.onBackground,
                     nav = nav,
                     route = Route.Chess,

amethyst/src/main/res/drawable/ic_chess.xml

@@ -1,9 +0,0 @@
-<vector xmlns:android="http://schemas.android.com/apk/res/android"
-    android:width="24dp"
-    android:height="24dp"
-    android:viewportWidth="24"
-    android:viewportHeight="24">
-  <path
-      android:fillColor="#FF9C9C9C"
-      android:pathData="M19,22H5v-2h14v2M17.16,8.26A8.94,8.94 0,0 0,19 3H15.03A5.24,5.24 0,0 1,14.05 4.89L10.08,4.89A5.24,5.24 0,0 1,9.1 3H5A8.94,8.94 0,0 0,6.84 8.26L6.84,18h10.32v-9.74ZM7.5,6c0.28,0 0.5,0.22 0.5,0.5S7.78,7 7.5,7 7,6.78 7,6.5 7.22,6 7.5,6M9,12 L9,9h2v3H9M13,12v-3h2v3H13Z"/>
-</vector>

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

@@ -59,6 +59,7 @@ object MaterialSymbols {
     val Chat = MaterialSymbol("\uE0C9")
     val Check = MaterialSymbol("\uE5CA")
     val CheckCircle = MaterialSymbol("\uF0BE")
+    val ChessKnight = MaterialSymbol("\uF25E")
     val Checklist = MaterialSymbol("\uE6B1")
     val ChevronRight = MaterialSymbol("\uE5CC")
     val Circle = MaterialSymbol("\uEF4A")