chore: 更新 .gitignore 排除构建产物和临时文件

添加 target/、*.class、__pycache__/、backend/uploads/、*.png 等规则

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/target/classes/application.yml

@@ -1,20 +0,0 @@
-server:
-  port: 8080
-
-spring:
-  datasource:
-    url: jdbc:mysql://localhost:3306/maternal_mall?useSSL=false&allowPublicKeyRetrieval=true&serverTimezone=Asia/Shanghai&characterEncoding=utf8
-    username: root
-    password: qq5211314
-  jpa:
-    hibernate:
-      ddl-auto: update
-    show-sql: false
-    properties:
-      hibernate:
-        format_sql: true
-  jackson:
-    time-zone: Asia/Shanghai
-
-app:
-  token-header: X-Token