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/pano.ts

@@ -0,0 +1,8 @@
+import type { Photo } from './types';
+
+export const PANO_TAG = 'pano360';
+
+export function isPanoTag(photo: Photo | null | undefined): boolean {
+	if (!photo?.tags?.length) return false;
+	return photo.tags.some((t) => t.name.trim().toLowerCase() === PANO_TAG);
+}