refactor: CSS残留hex清理+内联样式提取+console.log降级+错误toast补全

- components.css: 10处hex替换为CSS变量(stoploss/watch/signal/alert-change/toast)
- pages.css: 20+处hex替换(ss-dot信号强度/step操作色/summary-tag/trade-type/reason-item)
- auth.css: 2处hex替换(login-error/login-success)
- base.css: 新增30+公共CSS class(cursor-pointer/flex-center/input-mini/icon-sm等)
- index.html: 41处内联style提取为CSS class(93→52)
- app.js: 14处console.log降级为console.debug(减少生产日志噪音)
- app.js: 5处用户可感知catch块补充showToast错误反馈

stock-html/static/css/auth.css

@@ -120,14 +120,14 @@
 }
 
 .login-error {
-    color: #ff4444;
+    color: var(--danger);
     font-size: 13px;
     margin-bottom: 12px;
     text-align: center;
 }
 
 .login-success {
-    color: #00ff88;
+    color: var(--success);
     font-size: 13px;
     margin-bottom: 12px;
     text-align: center;