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/models/models.go

@@ -3,12 +3,13 @@ package models
 import "time"
 
 type User struct {
-	ID           string    `json:"id"`
-	Email        string    `json:"email"`
-	PasswordHash string    `json:"-"`
-	Name         string    `json:"name"`
-	AvatarURL    string    `json:"avatar_url,omitempty"`
-	CreatedAt    time.Time `json:"created_at"`
+	ID           string         `json:"id"`
+	Email        string         `json:"email"`
+	PasswordHash string         `json:"-"`
+	Name         string         `json:"name"`
+	AvatarURL    string         `json:"avatar_url,omitempty"`
+	Preferences  map[string]any `json:"preferences,omitempty"`
+	CreatedAt    time.Time      `json:"created_at"`
 }
 
 type PublicUser struct {