web: admin surfaces so the PhotoPrism UI is never needed

- Account tab in General settings — self-service password change.
- UsersDialog (admin-only footer entry) — full /api/v1/users CRUD with
  admin-issued password reset.
- People as a fifth tag category alongside Labels/Keywords/Colors/Ratings,
  backed by /api/v1/subjects and the `person:` DSL clause.
- About tab in Library settings — version, library counts, feature chips,
  and a collapsible env-config help panel for the bits PP has no runtime
  API for (OIDC, TF, WebDAV).
- Library tab expanded with Indexer-advanced, extra Downloads checksums,
  and a Features grid that only renders keys PhotoPrism actually returns.
- Fix the SettingsDialog null-draft race the same way GeneralSettingsDialog
  already had: normalize on open, never null on close.

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

web/src/routes/tags/[category]/[[value]]/+page.svelte

@@ -6,8 +6,10 @@
 		getPhoto,
 		listLabels,
 		listPhotos,
+		listSubjects,
 		type PhotoMarksMap,
-		type PpLabel
+		type PpLabel,
+		type PpSubject
 	} from '$lib/services/photoprism';
 	import {
 		filtersToQ,
@@ -65,7 +67,9 @@
 	// filter on top would make drill counts disagree with the badges (a
 	// label badge of 157 could otherwise drill into 0 photos because the
 	// session is scoped to a folder that has none of them).
-	const useServer = $derived(category === 'labels' || category === 'keywords');
+	const useServer = $derived(
+		category === 'labels' || category === 'keywords' || category === 'people'
+	);
 	const drillQ = $derived(
 		useServer && selectedValue
 			? filtersToQ({
@@ -128,6 +132,11 @@
 		queryFn: listLabels,
 		enabled: isAuthenticated() && category === 'labels'
 	}));
+	const subjectsQuery = createQuery<PpSubject[]>(() => ({
+		queryKey: ['subjects'],
+		queryFn: listSubjects,
+		enabled: isAuthenticated() && category === 'people'
+	}));
 	const drillTitle = $derived.by(() => {
 		if (!selectedValue) return '';
 		if (category === 'labels') {
@@ -137,6 +146,10 @@
 			return hit?.Name ?? selectedValue;
 		}
 		if (category === 'keywords') return selectedValue;
+		if (category === 'people') {
+			const hit = (subjectsQuery.data ?? []).find((s) => s.Slug === selectedValue);
+			return hit?.Name ?? selectedValue;
+		}
 		if (category === 'ratings') return starLabel(parseInt(selectedValue, 10));
 		if (category === 'colors') {
 			return (