fix: 修复暗色主题UI对比度、端口占用死循环及多项Web表单bug

后端修复:
- engine/instances.py: Socks5Server.start() 端口占用时死循环, 增加超时和异常透传
- engine/instances.py: import time 移至顶层
- engine/instances.py: sync_instances/start_instance 容忍单实例启动失败
- run.py: 启动时 sync_instances 失败不退出进程
- web/routes.py: instances start/restart/edit 路由捕获 OSError, flash 友好提示
- api/v1.py: instances start/restart/update API 返回 JSON 错误而非 500 崩溃
- web/routes.py: toggle_user/ban_user 支持 hidden 字段语义, 缺字段时切换状态
- web/routes.py: inject_nav 增加独立 nav.dashboard 和 page_name, 修复双 active bug
- auth.py: login 路由添加 logging import, 修 NameError

前端重构:
- templates/base.html: 全局对比度提升(--text #f1f5f9, --accent #a5b4fc), 标题色显式声明, alert/modal/progress/table 完整暗色样式
- templates/base.html: main-content padding-top 修复 navbar 遮挡内容
- templates/base.html: 侧边栏 active 高亮 (白字 + elevated bg + 左边框)
- templates/base.html: 顶栏动态显示当前页面名
- templates/*.html: 统一 page-header 类, 所有图标按钮添加 title tooltip
- templates/users.html: toggle/ban 表单添加 hidden enabled/ban 字段
- templates/connections.html: fmtBytes 改为 Jinja macro, 时间格式化
- templates/dashboard.html: 时间格式化为 YYYY-MM-DD HH:MM:SS, chart canvas 高度调整
- templates/logs.html: 时间格式化为可读格式
- templates/stats.html: 提升 chart 颜色对比度
- templates/system.html: 使用 time.localtime() 显示本地时间

templates/instances.html

@@ -2,8 +2,8 @@
 {% block title %}代理实例 · SOCKS Manager{% endblock %}
 
 {% block content %}
-<div class="d-flex justify-content-between align-items-center mb-3">
-  <h5 class="mb-0"><i class="bi bi-server"></i> 代理实例</h5>
+<div class="page-header">
+  <h5><i class="bi bi-server"></i> 代理实例</h5>
   <button class="btn btn-primary btn-sm" data-bs-toggle="modal" data-bs-target="#addInstanceModal">
     <i class="bi bi-plus-lg"></i> 新建实例</button>
 </div>
@@ -44,17 +44,17 @@
             <div class="btn-group btn-group-sm">
               {% if not inst.running %}
               <form method="post" action="/instances/{{ inst.id }}/start" style="display:inline">
-                <button class="btn btn-outline-success"><i class="bi bi-play-fill"></i></button>
+                <button class="btn btn-outline-success" title="启动"><i class="bi bi-play-fill"></i></button>
               </form>
               {% else %}
               <form method="post" action="/instances/{{ inst.id }}/stop" style="display:inline">
-                <button class="btn btn-outline-warning"><i class="bi bi-pause-fill"></i></button>
+                <button class="btn btn-outline-warning" title="停止"><i class="bi bi-pause-fill"></i></button>
               </form>
               <form method="post" action="/instances/{{ inst.id }}/restart" style="display:inline">
-                <button class="btn btn-outline-primary"><i class="bi bi-arrow-clockwise"></i></button>
+                <button class="btn btn-outline-primary" title="重启"><i class="bi bi-arrow-clockwise"></i></button>
               </form>
               {% endif %}
-              <button class="btn btn-outline-secondary" data-bs-toggle="modal"
+              <button class="btn btn-outline-secondary" title="编辑" data-bs-toggle="modal"
                       data-bs-target="#editInstanceModal"
                       data-name="{{ inst.name }}"
                       data-host="{{ inst.host }}"
@@ -70,7 +70,7 @@
               </button>
               <form method="post" action="/instances/{{ inst.id }}/delete" style="display:inline"
                     onsubmit="return confirmDelete('确认删除实例 {{ inst.name }}？')">
-                <button class="btn btn-outline-danger"><i class="bi bi-trash"></i></button>
+                <button class="btn btn-outline-danger" title="删除"><i class="bi bi-trash"></i></button>
               </form>
             </div>
           </td>