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/routes/+layout.svelte

@@ -15,7 +15,7 @@
 		if (auth.isAuthenticated && !auth.user) {
 			authApi
 				.me()
-				.then((data) => auth.setUser(data.user))
+				.then((data) => auth.setUser({ ...data.user, preferences: data.preferences ?? {} }))
 				.catch(() => {});
 		}
 	});