Redesign frontend UI with Observatory theme

New teal-accent color system, DM Sans + JetBrains Mono typography,
glow effects, animated gradient login page, animated dashboard counters
with gradient-border stat cards, event timeline, sidebar with active
glow indicators, and polished components (modals, cards, snackbar).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/app.html

@@ -4,6 +4,9 @@
 		<meta charset="utf-8" />
 		<meta name="viewport" content="width=device-width, initial-scale=1" />
 		<link rel="icon" type="image/svg+xml" href="/favicon.svg" />
+		<link rel="preconnect" href="https://fonts.googleapis.com" />
+		<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
+		<link href="https://fonts.googleapis.com/css2?family=DM+Sans:ital,opsz,wght@0,9..40,300..700;1,9..40,300..700&family=JetBrains+Mono:wght@400;500;600&display=swap" rel="stylesheet" />
 		<title>Immich Watcher</title>
 		%sveltekit.head%
 	</head>