Header round 6b (owner): the open-sidebar toggle matches the close glyph — size-4 both ways

The header toggle's PanelLeftOpenIcon was size-5 while the sidebar's
close icon was size-4 — the button visibly grew when the sidebar closed.
The small look is the standard: both glyphs are size-4 in identical
size-9 boxes now.

Live: open glyph 16px, close glyph 16px, button boxes 36px both states.
Gates: typecheck, lint, 469/469.

components/sidebar.tsx

@@ -63,7 +63,10 @@ export function SidebarToggle() {
 	if (open) return null;
 	return (
 		<Button variant="ghost" size="icon" aria-label="Open sidebar" onClick={toggle}>
-			<PanelLeftOpenIcon className="size-5" />
+			{/* Owner, round 6: size-4, SAME as the close glyph — the toggle
+			    must not grow when the sidebar is closed (it did: size-5 here).
+			    The small look is the standard, both directions. */}
+			<PanelLeftOpenIcon className="size-4" />
 		</Button>
 	);
 }