feat(v1.9.0): Bootstrap 5 迁移第 3/4、4/4 轮（抽屉、表单、大屏内部）

版本号保持 1.9.0，仍为纯前端改动：
- 日历抽屉：快速输入改 form-control，任务/到期列表改 Bootstrap list-group，加急标签改 badge
- 客户详情：套餐下拉、开始日、天数/次数、终止日统一 form-select / form-control
- 大屏内部：KPI 改 card，TOP 榜与今日列表改 list-group，加急改 badge；热力网格保留自绘
- app.css 增加 Bootstrap 收敛规则（list-group 透明背景、任务分隔线）

验证：无头 Chrome 实拍日历、客户详情、大屏三页（shots/bs3-*.png），页面正常渲染
数据库与业务逻辑零改动

internal/web/templates/pages/screen.html

@@ -26,16 +26,16 @@
   </header>
 
   <section class="scr-kpis">
-    <div class="kpi">
+    <div class="kpi card bg-body-tertiary border-secondary-subtle">
       <span>客户</span><b>{{.D.Stats.Customers}}</b><i>位</i>
     </div>
     <div class="kpi">
       <span>活跃订阅</span><b>{{.D.Stats.ActiveSubs}}</b><i>条</i>
     </div>
-    <div class="kpi kpi-hot">
+    <div class="kpi kpi-hot card bg-body-tertiary border-secondary-subtle">
       <span>今日到期</span><b>{{.D.Stats.DueToday}}</b><i>条</i>
     </div>
-    <div class="kpi kpi-warm">
+    <div class="kpi kpi-warm card bg-body-tertiary border-secondary-subtle">
       <span>7 天内到期</span><b>{{.D.Stats.Due7}}</b><i>条</i>
     </div>
   </section>
@@ -72,7 +72,7 @@
     <div class="panel panel-top card bg-body-tertiary border-secondary-subtle">
       <div class="panel-head"><h2>即将到期 TOP 10</h2><span>按剩余量排序</span></div>
       {{if .D.Top}}
-      <ol class="top-list">
+      <ol class="top-list list-group list-group-flush">
         {{range $i, $s := .D.Top}}
         <li class="top-item lv-{{$s.Eval.Level}}">
           <span class="rank">{{add $i 1}}</span>
@@ -97,7 +97,7 @@
         <span>{{len .D.DueToday}} 条</span>
       </div>
       {{if .D.DueToday}}
-      <ul class="today-list">
+      <ul class="today-list list-group list-group-flush">
         {{range .D.DueToday}}
         <li class="lv-{{.Eval.Level}}">
           <span class="tchip" style="--tag:{{.PackageColor}}"><b>{{.CustomerTail}}</b>{{.CustomerName}}</span>
@@ -123,7 +123,7 @@
           <span class="tchip" style="--tag:{{.PackageColor}}"><b>{{.CustomerTail}}</b>{{.CustomerName}}</span>
           <span class="pkg">{{.PackageName}}</span>
           <span class="asg{{if .AssigneeNone}} none{{end}}"><i style="background:{{.AssigneeHex}}"></i>{{.AssigneeLabel}}</span>
-          {{if .Urgent}}<span class="tag-urgent">加急</span>{{end}}
+          {{if .Urgent}}<span class="badge text-bg-danger tag-urgent">加急</span>{{end}}
           <span class="rem">{{.RemainShort}}</span>
         </li>
         {{end}}