feat(task): JIRA형 작업 — 설명·우선순위·라벨 필드 + 댓글 스레드

- ProjectTask에 description/priority/labels 추가
- TaskComment 모델 + 엔드포인트(GET/POST /tasks/{id}/comments, DELETE /comments/{id})
- 댓글 작성자=요청자, 삭제는 작성자 또는 관리자
- PATCH /tasks: labels/dependsOn JSON 슬라이스 map 패치 처리

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/models/models.go

@@ -28,7 +28,7 @@ func All() []interface{} {
 		&Attendance{}, &LeaveRequest{}, &OvertimeRequest{}, &WorkPolicy{}, &LeaveBalance{},
 		// slice 3 — projects
 		&Company{}, &Product{}, &Version{}, &Project{}, &ProjectMember{},
-		&ClientContact{}, &ProjectTask{}, &Contract{}, &ContractFile{}, &PaymentSplit{},
+		&ClientContact{}, &ProjectTask{}, &TaskComment{}, &Contract{}, &ContractFile{}, &PaymentSplit{},
 		// slice 4 — incentive
 		&IncentiveConfig{}, &PaymentStage{}, &UserIncentive{}, &QuarterlySettlement{},
 		// slice 5 — accounting

internal/models/project.go

@@ -97,8 +97,11 @@ type ProjectTask struct {
 	Base
 	ProjectID   string                      `gorm:"index" json:"projectId"`
 	Title       string                      `json:"title"`
-	Lane        string                      `json:"lane"`   // todo | doing | review | done
-	Start       string                      `json:"start"`  // YYYY-MM-DD
+	Description string                      `json:"description"` // 상세 설명 (JIRA형 카드 본문)
+	Lane        string                      `json:"lane"`        // todo | doing | review | done
+	Priority    string                      `json:"priority"`    // low | medium | high | urgent
+	Labels      datatypes.JSONSlice[string] `json:"labels"`      // 라벨/태그
+	Start       string                      `json:"start"`       // YYYY-MM-DD
 	End         string                      `json:"end"`
 	Assignee    string                      `json:"assignee"`
 	OrderIdx    int                         `json:"orderIdx"`
@@ -111,6 +114,17 @@ type ProjectTask struct {
 
 func (m *ProjectTask) BeforeCreate(*gorm.DB) error { m.ensureID(); return nil }
 
+// TaskComment is a JIRA-style comment thread on a task (작성자·본문·시각).
+type TaskComment struct {
+	Base
+	TaskID      string    `gorm:"index" json:"taskId"`
+	AuthorEmail string    `json:"authorEmail"`
+	Body        string    `json:"body"`
+	CreatedAt   time.Time `json:"createdAt"`
+}
+
+func (m *TaskComment) BeforeCreate(*gorm.DB) error { m.ensureID(); return nil }
+
 // Contract holds the [admin-only] commercial terms of a project. BE is the
 // break-even floor (손해가 안 나는 최소 금액). Exposed ONLY to admins.
 type Contract struct {