feat(preferences): configurable photo info attributes stored in user profile

- backend: users.preferences jsonb (migration 000004), Me returns preferences, PATCH /auth/me/preferences with validation (visible list + labels)
- frontend: gear in info section opens PhotoInfoSettingsDialog; base attribute set shown by default, remaining under ellipsis; per-attribute visibility and custom labels persisted to the profile; reset clears settings from the profile
- frontend: dialog has select-all/deselect-all icon buttons (no 'show all'); EXIF constants extracted to lib/exif.ts
- fix: render modal overlays via portal to document.body so they center in the viewport despite transformed panel/rail ancestors
- openspec: sync lightroom-workspace-ui artifacts (spec/design/proposal/tasks 9.8)

frontend/src/lib/api.ts

@@ -1,5 +1,6 @@
 import { goto } from '$app/navigation';
 import { auth, type Tokens, type User } from './stores/auth.svelte';
+import type { Preferences } from './types';
 
 export class ApiError extends Error {
 	status: number;
@@ -97,5 +98,10 @@ export const authApi = {
 		}),
 	logout: (refresh_token: string) =>
 		api('/auth/logout', { method: 'POST', body: { refresh_token } }),
-	me: () => api<{ user: User }>('/auth/me')
+	me: () => api<{ user: User; preferences?: Preferences }>('/auth/me'),
+	savePreferences: (preferences: Preferences) =>
+		api<{ preferences: Preferences }>('/auth/me/preferences', {
+			method: 'PATCH',
+			body: preferences
+		})
 };