ui: separate trackers from projects; keep header dropdown on top

- /trackers index, Trackers section on the homepage and in the header nav;
  /projects lists only projects (tracker URLs unchanged)
- header is its own z-50 layer and <main> is isolated, so maps, charts and
  sticky tables no longer paint over the nav dropdowns

src/routes/trackers/+page.svelte

@@ -0,0 +1,12 @@
+<script lang="ts">
+	import CatalogGrid from '#lib/components/CatalogGrid.svelte';
+	import { trackers } from '#lib/projects.js';
+</script>
+
+<div class="mx-auto max-w-6xl px-4 py-12 sm:px-6 sm:py-16">
+	<h1 class="mb-3 text-4xl font-semibold tracking-tight sm:text-5xl">trackers</h1>
+	<p class="mb-10 text-[var(--site-muted)]">
+		Personal data I keep track of: games, money, houses, prices, animals and lists.
+	</p>
+	<CatalogGrid items={trackers} />
+</div>