fix: scope marks, labels, and subjects to the authenticated user

Marks (ratings/color labels) were stored without a user column — every
user saw every other user's marks. Labels and subjects from PhotoPrism's
global endpoints leaked across users because those endpoints ignore
BasePath ACL.

Sidecar:
- Add UserName as composite primary key on Mark (photo_uid, user_name)
- Replace validateSession with resolveSession that fetches the user
  identity from PhotoPrism's session endpoint
- Filter all mark queries by user_name

Frontend:
- Filter listLabels/listSubjects through a BasePath-aware existence
  check — each label/subject is kept only if the user has at least one
  matching photo (single count=1 probe per item, batched at concurrency 8)
- Skip filtering for admin users with empty BasePath (single-user compat)

Also documents USER_BASEPATHS in .env.example — the env var that drives
per-user library isolation via PhotoPrism's auth_users.base_path.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/lib/services/photoprism.ts

@@ -635,6 +635,35 @@ export async function aggregateKeywords(): Promise<AggregatedKeyword[]> {
 	return Array.from(buckets.values()).sort((a, b) => b.count - a.count);
 }
 
+async function hasPhotosMatching(q: string): Promise<boolean> {
+	const resp = await http.get<PpPhoto[]>('/photos', {
+		params: { count: 1, offset: 0, q }
+	});
+	return Array.isArray(resp.data) && resp.data.length > 0;
+}
+
+async function filterByUserPhotos<T>(
+	items: T[],
+	queryFor: (item: T) => string
+): Promise<T[]> {
+	if (userBasePath() === '') return items;
+	const CONCURRENCY = 8;
+	const out: T[] = [];
+	for (let i = 0; i < items.length; i += CONCURRENCY) {
+		const batch = items.slice(i, i + CONCURRENCY);
+		const checks = await Promise.all(
+			batch.map(async (item) => ({
+				item,
+				has: await hasPhotosMatching(queryFor(item))
+			}))
+		);
+		for (const { item, has } of checks) {
+			if (has) out.push(item);
+		}
+	}
+	return out;
+}
+
 export async function listLabels(): Promise<PpLabel[]> {
 	// `all=true` includes labels PhotoPrism has soft-deleted (auto-hidden
 	// low-confidence classifier hits, manually-removed labels). They're
@@ -646,7 +675,7 @@ export async function listLabels(): Promise<PpLabel[]> {
 	const { data } = await http.get<PpLabel[]>('/labels', {
 		params: { count: 1000, order: 'count', all: true }
 	});
-	return data;
+	return filterByUserPhotos(data, (l) => `label:${l.Slug}`);
 }
 
 // ── Subjects (people / face recognition) ────────────────────────────────────
@@ -670,7 +699,7 @@ export async function listSubjects(): Promise<PpSubject[]> {
 	const { data } = await http.get<PpSubject[]>('/subjects', {
 		params: { count: 1000, order: 'count' }
 	});
-	return data ?? [];
+	return filterByUserPhotos(data ?? [], (s) => `person:${s.Slug}`);
 }
 
 export async function updateSubject(uid: string, patch: Partial<PpSubject>): Promise<PpSubject> {