feat: add lock icons to restricted links on homepage

Add small lock icons in the top right corner of links that require authentication (streaming, family photos, cloud, shopping, family tree, transmission, documents, and audiobooks). The icons use SVG symbol references for efficient reuse and adapt to dark mode automatically.

src/lib/components/LinksGrid.svelte

@@ -46,6 +46,7 @@
 	transition: 200ms;
 	width: 100%;
 	padding: 1rem;
+	position: relative;
 }
 :global(.links_grid a:hover){
 	scale: 1.02;
@@ -57,11 +58,23 @@
 :global(.links_grid h3){
 	font-size: 1.5rem;
 }
+:global(.links_grid a .lock-icon){
+	position: absolute;
+	top: 0.5rem;
+	right: 0.5rem;
+	width: 1.5rem;
+	height: 1.5rem;
+	fill: var(--nord0);
+	opacity: 0.6;
+}
 
 @media (prefers-color-scheme: dark){
 	:global(.links_grid h3){
 		color: white;
 	}
+	:global(.links_grid a .lock-icon){
+		fill: white;
+	}
 	:global(.links_grid a:nth-child(4n)),
 	:global(.links_grid a:nth-child(4n) svg){
 		background-color: var(--nord6-dark);