Refactor user privilege handling to use Optional instead of null checks. Remove unused cache entries and update security configuration to refine access controls.

database/src/main/java/com/alttd/altitudeweb/database/web_db/PrivilegedUserMapper.java

@@ -1,8 +1,10 @@
 package com.alttd.altitudeweb.database.web_db;
 
 import org.apache.ibatis.annotations.*;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.List;
+import java.util.Optional;
 
 public interface PrivilegedUserMapper {
 
@@ -23,7 +25,7 @@ public interface PrivilegedUserMapper {
             @Result(property = "permissions", column = "id", javaType = List.class,
                     many = @Many(select = "getPermissionsForUser"))
     })
-    PrivilegedUser getUserByUuid(@Param("uuid") String uuid);
+    Optional<PrivilegedUser> getUserByUuid(@Param("uuid") String uuid);
 
     /**
      * Retrieves all privileged users with their permissions