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/users.html

@@ -2,7 +2,7 @@
 {% block title %}用户管理 · SOCKS Manager{% endblock %}
 
 {% block content %}
-<div class="d-flex justify-content-between align-items-center mb-3">
+<div class="page-header">
   <div>
     <h5 class="mb-0"><i class="bi bi-people"></i> 用户管理</h5>
     <span class="text-muted small">共 {{ total }} 个用户</span>
@@ -11,7 +11,7 @@
     <form method="get" class="d-flex">
       <input name="search" class="form-control form-control-sm" placeholder="搜索用户名"
              value="{{ search }}" style="width:180px">
-      <button type="submit" class="btn btn-outline-secondary btn-sm"><i class="bi bi-search"></i></button>
+      <button type="submit" class="btn btn-outline-secondary btn-sm" title="搜索"><i class="bi bi-search"></i></button>
     </form>
     <button class="btn btn-primary btn-sm" data-bs-toggle="modal" data-bs-target="#addUserModal">
       <i class="bi bi-plus-lg"></i> 新建用户</button>
@@ -55,7 +55,7 @@
           <td><small class="text-muted">{{ u.created_at[:10] }}</small></td>
           <td>
             <div class="btn-group btn-group-sm">
-              <button class="btn btn-outline-secondary" data-bs-toggle="modal" data-bs-target="#editUserModal"
+              <button class="btn btn-outline-secondary" title="编辑" data-bs-toggle="modal" data-bs-target="#editUserModal"
                       data-id="{{ u.id }}"
                       data-username="{{ u.username }}"
                       data-bw-down="{{ u.bandwidth_down }}"
@@ -69,18 +69,22 @@
                 <i class="bi bi-pencil"></i>
               </button>
               <form method="post" action="/users/{{ u.id }}/toggle" style="display:inline">
-                <button class="btn btn-outline-{{ 'warning' if u.enabled else 'success' }}">
+                <input type="hidden" name="enabled" value="{{ 'false' if u.enabled else 'true' }}">
+                <button class="btn btn-outline-{{ 'warning' if u.enabled else 'success' }}"
+                        title="{{ '禁用' if u.enabled else '启用' }}">
                   <i class="bi bi-{{ 'eye-slash' if u.enabled else 'eye' }}"></i>
                 </button>
               </form>
               <form method="post" action="/users/{{ u.id }}/ban" style="display:inline">
-                <button class="btn btn-outline-{{ 'warning' if not u.banned else 'secondary' }}">
+                <input type="hidden" name="ban" value="{{ 'false' if u.banned else 'true' }}">
+                <button class="btn btn-outline-{{ 'warning' if not u.banned else 'secondary' }}"
+                        title="{{ '封禁' if not u.banned else '解封' }}">
                   <i class="bi bi-{{ 'ban' if not u.banned else 'check-circle' }}"></i>
                 </button>
               </form>
               <form method="post" action="/users/{{ u.id }}/delete" style="display:inline"
                     onsubmit="return confirmDelete('确认删除用户 {{ u.username }}？')">
-                <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>