Add MDI icon picker to all entity types

- Install @mdi/js (~7000 Material Design Icons)
- IconPicker component: dropdown with search, popular icons grid,
  clear option. Stores icon name as string (e.g. "mdiCamera")
- MdiIcon component: renders SVG from icon name
- Backend: add `icon` field to ImmichServer, TelegramBot,
  TrackingConfig, TemplateConfig, NotificationTarget, AlbumTracker
- All 6 entity pages: icon picker next to name input in create/edit
  forms, icon displayed on entity cards

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

frontend/src/lib/components/MdiIcon.svelte

@@ -0,0 +1,13 @@
+<script lang="ts">
+	import * as mdi from '@mdi/js';
+
+	let { name = '', size = 18 } = $props<{ name: string; size?: number }>();
+
+	function getPath(iconName: string): string {
+		return (mdi as any)[iconName] || '';
+	}
+</script>
+
+{#if name && getPath(name)}
+	<svg viewBox="0 0 24 24" width={size} height={size} fill="currentColor"><path d={getPath(name)} /></svg>
+{/if}