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/routes/login/+page.svelte

@@ -61,8 +61,8 @@
 		class="w-full max-w-sm space-y-5 rounded-lg border border-border bg-card p-8 shadow-sm"
 	>
 		<header class="space-y-1">
-			<h1 class="text-2xl font-semibold tracking-tight text-foreground">Mule</h1>
-			<p class="text-sm text-muted-foreground">Sign in with your PhotoPrism account.</p>
+			<h1 class="text-2xl font-semibold tracking-tight text-foreground">Mulimage</h1>
+			<p class="text-sm text-muted-foreground">Sign in to your account.</p>
 		</header>
 
 		<label class="block space-y-1.5">