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)

backend/internal/app/app.go

@@ -115,6 +115,7 @@ func (s *Server) Router() *gin.Engine {
 	authed.Use(s.auth.Middleware())
 
 	authed.GET("/auth/me", authHandler.Me)
+	authed.PATCH("/auth/me/preferences", authHandler.UpdatePreferences)
 	authed.GET("/sse/albums/:id", s.albumSSE)
 	authed.GET("/sse/me", s.meSSE)