feat: v1.5 安全加固与体验优化

- 后端添加 express-rate-limit 限流（登录 10次/分钟，API 200次/分钟）
- H5 演示登录：自动获取 demo token，401 时自动重试
- 分类删除前查询关联记录数，提示用户影响范围
- 分类添加支持 8 色选择器，替代随机颜色
- 首页 overview card 改为日均+收入+笔数，避免重复显示支出
- 请求模块 401 处理优化：H5 自动刷新 token 并重试原请求

server/package-lock.json

@@ -11,6 +11,7 @@
         "cors": "^2.8.5",
         "dotenv": "^17.4.2",
         "express": "^4.18.2",
+        "express-rate-limit": "^8.5.2",
         "mysql2": "^3.9.0"
       },
       "devDependencies": {
@@ -1042,6 +1043,24 @@
         "url": "https://opencollective.com/express"
       }
     },
+    "node_modules/express-rate-limit": {
+      "version": "8.5.2",
+      "resolved": "https://registry.npmjs.org/express-rate-limit/-/express-rate-limit-8.5.2.tgz",
+      "integrity": "sha512-5Kb34ipNX694DH48vN9irak1Qx30nb0PLYHXfJgw4YEjiC3ZEmZJhwOp+VfiCYwFzvFTdB9QkArYS5kXa2cx2A==",
+      "license": "MIT",
+      "dependencies": {
+        "ip-address": "^10.2.0"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/express-rate-limit"
+      },
+      "peerDependencies": {
+        "express": ">= 4.11"
+      }
+    },
     "node_modules/fast-glob": {
       "version": "3.3.3",
       "resolved": "https://registry.npmjs.org/fast-glob/-/fast-glob-3.3.3.tgz",
@@ -1298,6 +1317,15 @@
         "node": ">= 0.10"
       }
     },
+    "node_modules/ip-address": {
+      "version": "10.2.0",
+      "resolved": "https://registry.npmjs.org/ip-address/-/ip-address-10.2.0.tgz",
+      "integrity": "sha512-/+S6j4E9AHvW9SWMSEY9Xfy66O5PWvVEJ08O0y5JGyEKQpojb0K0GKpz/v5HJ/G0vi3D2sjGK78119oXZeE0qA==",
+      "license": "MIT",
+      "engines": {
+        "node": ">= 12"
+      }
+    },
     "node_modules/ipaddr.js": {
       "version": "1.9.1",
       "resolved": "https://registry.npmjs.org/ipaddr.js/-/ipaddr.js-1.9.1.tgz",