Refactor and improve code consistency across multiple files

- Enhanced SQL queries in `session.go` and `share.go` for clarity and consistency.
- Updated comments for better understanding and maintenance.
- Ensured consistent error handling and return statements across various methods.

backend/internal/handlers/errors.go

@@ -91,5 +91,5 @@ func respondInternalError(c *gin.Context, message string, err error) {
 	respondWithError(c, http.StatusInternalServerError, "internal_error", message)
 }
 func respondInvalidID(c *gin.Context, message string) {
-    respondWithError(c, http.StatusBadRequest, "invalid_id", message)
+	respondWithError(c, http.StatusBadRequest, "invalid_id", message)
 }