Fix sidenav collapse button flash on mobile

Doubled CSS selector specificity to ensure display: none beats
Button.module.css's display: flex regardless of load order.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.beans/sendou.ink-ekv0--collapse-sidenav-button-flashes-on-mobile-page-loa.md

@@ -1,10 +1,11 @@
 ---
 # sendou.ink-ekv0
 title: Collapse sidenav button flashes on mobile page load
-status: todo
+status: completed
 type: bug
+priority: normal
 created_at: 2026-01-15T19:16:35Z
-updated_at: 2026-01-15T19:16:35Z
+updated_at: 2026-01-17T06:04:49Z
 ---
 
 The collapse sidenav button should not be visible on mobile at all, but it currently flashes briefly during page load before being hidden. It should not show even for a fraction of a second.

app/components/layout/index.module.css

@@ -110,7 +110,8 @@
 	padding: var(--s-1) var(--s-2);
 }
 
-.sideNavCollapseButton {
+/* Doubled selector increases specificity to beat Button.module.css's display: flex */
+.sideNavCollapseButton.sideNavCollapseButton {
 	display: none;
 
 	& svg {
@@ -121,7 +122,7 @@
 }
 
 @media screen and (min-width: 600px) {
-	.sideNavCollapseButton {
+	.sideNavCollapseButton.sideNavCollapseButton {
 		display: flex;
 	}
 }