feat(nav): add hover state on inactive tablet and desktop nav items

Applies hover:bg-[var(--color-subtle)] to inactive nav links for
visual feedback on pointer devices.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/nav/DesktopSidebar.svelte

@@ -30,7 +30,7 @@
 					aria-current={active ? 'page' : undefined}
 					class="px-3 py-[7px] text-[13px] font-[var(--font-sans)] rounded-[var(--radius-md)] flex items-center gap-2 {active
 						? 'bg-[var(--green-tint)] text-[var(--green-dark)] font-medium'
-						: ''}"
+						: 'hover:bg-[var(--color-subtle)]'}"
 				>
 					<span class="w-[20px] text-[16px] text-center">{item.icon}</span>
 					{item.label}

frontend/src/lib/nav/TabletNavBar.svelte

@@ -14,7 +14,7 @@
 			aria-current={active ? 'page' : undefined}
 			class="px-4 py-2 rounded-[var(--radius-md)] text-[13px] font-[var(--font-sans)] {active
 				? 'bg-[var(--green-tint)] text-[var(--green-dark)] font-medium'
-				: ''}"
+				: 'hover:bg-[var(--color-subtle)]'}"
 		>
 			<span>{item.icon}</span>
 			{item.label}