refactor: improve question service entity types and security config

- Change Question entity time fields from Date to LocalDateTime for Java 8+ time API consistency
- Add auto-fill annotation for updateTime field in Question and QuestionSubmit entities
- Simplify Serializable import in QuestionQueryRequestDTO
- Temporarily set SecurityConfiguration to permit all requests for development
- Remove generated .flattened-pom.xml build artifacts from version control

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

aioj-backend-common/aioj-backend-common-security/src/main/java/cn/meowrain/aioj/backend/framework/security/config/SecurityConfiguration.java

@@ -53,7 +53,7 @@ public class SecurityConfiguration {
 				.permitAll()
 				// 其他请求需要认证（可由子类覆盖此配置）
 				.anyRequest()
-				.authenticated())
+				.permitAll())
 			.addFilterBefore(jwtAuthenticationFilter, UsernamePasswordAuthenticationFilter.class);
 		return http.build();
 	}