feat(ui): 360 panorama viewer by pano360 tag

- Detect 'pano360' tag and open the photo in a spherical viewer
- Mini-WebGL equirect viewer (no deps): drag to look, wheel FOV, Space reset
- Load original as origin-clean bitmap; fall back to flat image without WebGL
- 360 indicator in viewer and badge on grid tiles

frontend/src/lib/components/PhotoGrid.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
 	import Icon from './Icon.svelte';
 	import { density } from '$lib/stores/density.svelte';
+	import { isPanoTag } from '$lib/pano';
 	import type { Photo } from '$lib/types';
 
 	interface Props {
@@ -74,6 +75,14 @@
 							обработка…
 						</span>
 					{/if}
+					{#if isPanoTag(photo)}
+						<span
+							class="bg-bg/70 text-text absolute top-1 left-1 rounded px-1.5 py-0.5 text-[10px] font-semibold"
+							aria-label="360-панорама"
+						>
+							360
+						</span>
+					{/if}
 					<span
 						class="bg-bg/70 text-text absolute right-1 bottom-1 flex items-center gap-1.5 rounded px-1.5 py-0.5 text-xs"
 					>