refactor(achievement): extract achievement logic into AchievementService

Move EnsureExists + GetAllScores + compute loop from handler into
AchievementService.GetAll, and validation + ensure + increment into
AchievementService.Increment. Handlers now delegate to the service
layer for business logic while retaining protocol response building.

GetAchData stays as a pure function in handlers_achievement.go per plan.

server/channelserver/svc_achievement.go

@@ -0,0 +1,62 @@
+package channelserver
+
+import (
+	"fmt"
+
+	"go.uber.org/zap"
+)
+
+// AchievementService encapsulates business logic for the achievement system.
+type AchievementService struct {
+	achievementRepo AchievementRepo
+	logger          *zap.Logger
+}
+
+// NewAchievementService creates a new AchievementService.
+func NewAchievementService(ar AchievementRepo, log *zap.Logger) *AchievementService {
+	return &AchievementService{achievementRepo: ar, logger: log}
+}
+
+const achievementEntryCount = uint8(33)
+
+// AchievementSummary holds the computed achievements and total points for a character.
+type AchievementSummary struct {
+	Points       uint32
+	Achievements [33]Achievement
+}
+
+// GetAll ensures the achievement record exists, fetches all scores, and computes
+// the achievement state for every category. Returns the total accumulated points
+// and per-category Achievement data.
+func (svc *AchievementService) GetAll(charID uint32) (*AchievementSummary, error) {
+	if err := svc.achievementRepo.EnsureExists(charID); err != nil {
+		svc.logger.Error("Failed to ensure achievements record", zap.Error(err))
+	}
+
+	scores, err := svc.achievementRepo.GetAllScores(charID)
+	if err != nil {
+		return nil, err
+	}
+
+	var summary AchievementSummary
+	for id := uint8(0); id < achievementEntryCount; id++ {
+		ach := GetAchData(id, scores[id])
+		summary.Points += ach.Value
+		summary.Achievements[id] = ach
+	}
+	return &summary, nil
+}
+
+// Increment validates the achievement ID, ensures the record exists, and bumps
+// the score for the given achievement category.
+func (svc *AchievementService) Increment(charID uint32, achievementID uint8) error {
+	if achievementID > 32 {
+		return fmt.Errorf("achievement ID %d out of range [0, 32]", achievementID)
+	}
+
+	if err := svc.achievementRepo.EnsureExists(charID); err != nil {
+		svc.logger.Error("Failed to ensure achievements record", zap.Error(err))
+	}
+
+	return svc.achievementRepo.IncrementScore(charID, achievementID)
+}