feat(orgchart): Introduce standalone orgchart RP and shared link public API

This commit includes:
- Added SharedLink data model and Keto-bypassed public API for orgchart view
- Configured 'orgfront' as a new OAuth2 client in hydra
- Applied MH Dashboard premium beige theme to OrgChart
- Implemented user lookup fallback to company code

backend/internal/domain/shared_link.go

@@ -0,0 +1,53 @@
+package domain
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"time"
+
+	"github.com/google/uuid"
+	"gorm.io/gorm"
+)
+
+type SharedLink struct {
+	ID          string         `gorm:"primaryKey;type:uuid;default:gen_random_uuid()" json:"id"`
+	TenantID    string         `gorm:"type:uuid;not null;index" json:"tenantId"`
+	Token       string         `gorm:"uniqueIndex;not null" json:"token"`
+	Name        string         `gorm:"not null" json:"name"` // 링크 식별을 위한 이름 (예: "24년 상반기 채용공고용")
+	Description string         `json:"description"`
+	AccessLevel string         `gorm:"default:'READ_ONLY'" json:"accessLevel"`
+	IsActive    bool           `gorm:"default:true" json:"isActive"`
+	ExpiresAt   *time.Time     `json:"expiresAt"`
+	Password    string         `json:"-"` // 필요 시 비밀번호 (선택 사항)
+	CreatedAt   time.Time      `json:"createdAt"`
+	UpdatedAt   time.Time      `json:"updatedAt"`
+	DeletedAt   gorm.DeletedAt `gorm:"index" json:"-"`
+
+	// Relation
+	Tenant Tenant `gorm:"foreignKey:TenantID" json:"-"`
+}
+
+func (s *SharedLink) BeforeCreate(tx *gorm.DB) (err error) {
+	if s.ID == "" {
+		s.ID = uuid.NewString()
+	}
+	if s.Token == "" {
+		// 32바이트(64자)의 강력한 난수 토큰 생성
+		b := make([]byte, 32)
+		if _, err := rand.Read(b); err != nil {
+			return err
+		}
+		s.Token = hex.EncodeToString(b)
+	}
+	return
+}
+
+func (s *SharedLink) IsValid() bool {
+	if !s.IsActive {
+		return false
+	}
+	if s.ExpiresAt != nil && s.ExpiresAt.Before(time.Now()) {
+		return false
+	}
+	return true
+}