refactor: extract explorer open gesture and standardize icon sizes

packages/app/src/components/headers/back-header.tsx

@@ -26,7 +26,7 @@ export function BackHeader({
             onPress={onBack ?? (() => router.back())}
             style={styles.backButton}
           >
-            <ArrowLeft size={20} color={theme.colors.foregroundMuted} />
+            <ArrowLeft size={theme.iconSize.lg} color={theme.colors.foregroundMuted} />
           </Pressable>
           {title && (
             <Text style={styles.title} numberOfLines={1}>

packages/app/src/components/headers/menu-header.tsx

@@ -75,7 +75,7 @@ export function SidebarMenuToggle({
       {isMobile ? (
         <MobileMenuIcon color={menuIconColor} />
       ) : (
-        <PanelLeft size={16} color={menuIconColor} />
+        <PanelLeft size={theme.iconSize.md} color={menuIconColor} />
       )}
     </HeaderToggleButton>
   );