web: de-brand PhotoPrism references in user-facing copy

Replaces "PhotoPrism" in UI strings (empty states, tooltips, toasts,
log header, login screen) with neutral terms like "the indexer", "the
library", "the server" — accurate regardless of backend. The login
header becomes "Mulimage" and drops the explicit PhotoPrism mention.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/actions/gridKeyNav.ts

@@ -333,7 +333,7 @@ export function gridKeyNav(node: HTMLElement, params: GridKeyNavParams = {}) {
 			// truth.
 			if (added.length === 0) {
 				toast.error(`Nothing added to ${heap.Title}`, {
-					description: `PhotoPrism rejected all ${ids.length} UIDs (already in heap, or not indexed).`
+					description: `The server rejected all ${ids.length} UIDs (already in heap, or not indexed).`
 				});
 				return;
 			}