[BE-API-023] be-api: Implement user completion endpoint validation

- Standardized GetProfileCompletion handler to use GetUserIDUUID
- Added validation to ensure completion percentage is between 0 and 100
- Handler already existed and was working correctly
- Endpoint returns correct completion percentage (0-100) and missing fields
- Handler uses standard API response format

Phase: PHASE-2
Priority: P1
Progress: 32/267 (12.0%)

VEZA_COMPLETE_MVP_TODOLIST.json

@@ -2130,7 +2130,17 @@
       "description": "Verify GET /api/v1/users/:id/completion returns correct completion percentage",
       "owner": "backend",
       "estimated_hours": 2,
-      "status": "todo",
+      "status": "completed",
+      "completion": {
+        "completed_at": "2025-12-23T10:03:30Z",
+        "actual_hours": 0.5,
+        "commits": [],
+        "files_changed": [
+          "veza-backend-api/internal/handlers/profile_handler.go"
+        ],
+        "notes": "Standardized GetProfileCompletion handler to use GetUserIDUUID instead of c.Get. Added validation to ensure completion percentage is between 0 and 100. Handler already existed and was working correctly. The CalculateProfileCompletion service method correctly calculates percentage as (completedFields * 100) / totalFields. Endpoint returns correct completion percentage (0-100) and list of missing fields. Handler uses standard API response format (RespondSuccess, RespondWithAppError).",
+        "issues_encountered": []
+      },
       "files_involved": [],
       "implementation_steps": [
         {

veza-backend-api/internal/handlers/profile_handler.go

@@ -118,6 +118,8 @@ func (h *ProfileHandler) GetProfileByUsername(c *gin.Context) {
 }
 
 // GetProfileCompletion retrieves the profile completion status
+// GET /api/v1/users/:id/completion
+// BE-API-023: Implement user completion endpoint validation
 // T0220: Returns percentage and missing fields
 // @Summary      Get Profile Completion
 // @Description  Get profile completion percentage and missing fields
@@ -134,22 +136,14 @@ func (h *ProfileHandler) GetProfileCompletion(c *gin.Context) {
 	userIDStr := c.Param("id")
 	userID, err := uuid.Parse(userIDStr)
 	if err != nil {
-		RespondWithAppError(c, apperrors.New(apperrors.ErrCodeValidation, "invalid user id"))
+		RespondWithAppError(c, apperrors.NewValidationError("invalid user id"))
 		return
 	}
 
 	// Get authenticated user ID
-	var authenticatedUserID uuid.UUID
-	if reqID, exists := c.Get("user_id"); exists {
-		if reqUUID, ok := reqID.(uuid.UUID); ok {
-			authenticatedUserID = reqUUID
-		} else {
-			RespondWithAppError(c, apperrors.NewUnauthorizedError("user not authenticated"))
-			return
-		}
-	} else {
-		RespondWithAppError(c, apperrors.NewUnauthorizedError("user not authenticated"))
-		return
+	authenticatedUserID, ok := GetUserIDUUID(c)
+	if !ok {
+		return // Erreur déjà envoyée par GetUserIDUUID
 	}
 
 	// Verify that user_id corresponds to authenticated user
@@ -161,10 +155,27 @@ func (h *ProfileHandler) GetProfileCompletion(c *gin.Context) {
 	// Calculate profile completion
 	completion, err := h.userService.CalculateProfileCompletion(userID)
 	if err != nil {
-		RespondWithAppError(c, apperrors.New(apperrors.ErrCodeInternal, "failed to calculate profile completion"))
+		if err.Error() == "user not found" {
+			RespondWithAppError(c, apperrors.NewNotFoundError("user"))
+			return
+		}
+		RespondWithAppError(c, apperrors.Wrap(apperrors.ErrCodeInternal, "failed to calculate profile completion", err))
 		return
 	}
 
+	// Verify that percentage is between 0 and 100
+	if completion.Percentage < 0 || completion.Percentage > 100 {
+		h.logger.Warn("Invalid completion percentage calculated",
+			zap.Int("percentage", completion.Percentage),
+			zap.String("user_id", userID.String()))
+		// Clamp to valid range
+		if completion.Percentage < 0 {
+			completion.Percentage = 0
+		} else if completion.Percentage > 100 {
+			completion.Percentage = 100
+		}
+	}
+
 	RespondSuccess(c, http.StatusOK, completion)
 }