fix: 成长报告海报用宠物真实头像（没传才用 emoji）

- 后端 Poster 增 pet_avatar_url（取 pet.AvatarURL，和身份卡同一可靠路径）
- 海报 canvas 优先用它、store 兜底；有照片画圆形头像、没有才 emoji
- 头像九参数居中裁剪，竖图/横图都不压扁

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

pets-be/internal/service/report.go

@@ -199,6 +199,7 @@ func (s *Service) GetHealthSummary(userID, petID string) (*HealthSummary, error)
 type Poster struct {
 	PetName         string `json:"pet_name"`
 	PetEmoji        string `json:"pet_emoji"`
+	PetAvatarURL    string `json:"pet_avatar_url"` // 上传过照片就有，海报优先用它，没有才用 emoji
 	Age             string `json:"age"`
 	Weight          string `json:"weight"`
 	Stage           string `json:"stage"`
@@ -223,7 +224,8 @@ func (s *Service) GetPoster(userID, petID string) (*Poster, error) {
 	s.db.Model(&model.HealthRecord{}).Where("pet_id = ? AND type = ?", petID, model.RecordVaccine).Count(&vaccineRecs)
 
 	return &Poster{
-		PetName: pet.Name, PetEmoji: pet.Emoji, Age: pet.Age, Weight: pet.Weight, Stage: pet.Stage,
+		PetName: pet.Name, PetEmoji: pet.Emoji, PetAvatarURL: pet.AvatarURL,
+		Age: pet.Age, Weight: pet.Weight, Stage: pet.Stage,
 		TasksCompleted: tasksDone, WeightRecords: weightRecs, VaccineRecords: vaccineRecs,
 		HighRiskCount: 0, Headline: "稳定成长",
 	}, nil