feat(v1.6): 键盘 3×4、格子计数排版、时钟修复、已完成折叠、静态资源破缓存

1) 触摸小键盘
- 改为 3 列 × 4 行，底行 ⌫ / 0 / ✓（数字 1-9 按 123/456/789 排列）
- 自定义按键样式：52px 高、圆角、按下位移反馈，确认键为主题绿，不再使用原生按钮外观

2) 日历格子
- 「待完成 / 总数」改为 34px 粗体、主题绿、靠左、垂直居中；左侧打手色竖条保留
- 仍不显示排单缩略信息

3) 抽屉时钟
- 修复不显示：根因是浏览器缓存了旧的 app.js（静态资源 max-age=300）
- 所有 CSS/JS 链接改为 /static/app.css?v=<版本号>，升级后自动取新文件
- 字号放大到 30px、水平垂直居中、24 小时制精确到秒，日期小字放在下方

4) 已完成排单折叠
- 当日清单里已完成/已跳过的单子折叠成一行：尾号 + 姓名 + 套餐 + 状态
- 点这一行展开，显示剩余、打手、撤销打卡与⋯菜单（加急/追加）；未完成的行不变
- 折叠箭头改为 CSS 三角，展开/收起有过渡动画

5) 背景
- 管理端背景横线彻底移除（已用浏览器截图确认），大屏网格背景保留

验证：
- 无头 Chrome 实拍暗色/亮色两套日历页（shots/v16-dark.png、shots/v16-light.png）
- 界面断言 14 项全部通过；原有 119 项验收回归全绿；go vet / go test ./... 通过
- 版本号 1.6.0

internal/web/templates/pages/calendar.html

@@ -63,7 +63,10 @@
     </div>
 
     <aside class="drawer">
-      <div class="drawer-clock"><b data-clock>--:--:--</b><span>{{.D.TodayStr}}</span></div>
+      <div class="drawer-clock">
+        <b data-clock>--:--:--</b>
+        <span>{{.D.TodayStr}}</span>
+      </div>
       <header class="drawer-head">
         <h2>{{.D.SelectedLabel}}</h2>
         <div class="drawer-tags">
@@ -83,19 +86,19 @@
           <button class="btn btn-sm btn-primary" type="submit">完成</button>
         </form>
         <p class="muted small quick-hint">唯一匹配直接完成；同尾号多人 / 一单多服务会列出让你勾选。</p>
-        <div class="keypad" data-keypad aria-label="数字小键盘">
-          <button type="button" data-key="1">1</button>
-          <button type="button" data-key="2">2</button>
-          <button type="button" data-key="3">3</button>
-          <button type="button" data-key="4">4</button>
-          <button type="button" data-key="5">5</button>
-          <button type="button" data-key="6">6</button>
-          <button type="button" data-key="7">7</button>
-          <button type="button" data-key="8">8</button>
-          <button type="button" data-key="9">9</button>
-          <button type="button" data-key="0">0</button>
-          <button type="button" data-key="back" class="key-back" aria-label="退格">⌫</button>
-          <button type="button" data-key="ok" class="key-ok" aria-label="确认完成">✓</button>
+        <div class="keypad" data-keypad role="group" aria-label="数字小键盘">
+          <button type="button" class="key" data-key="1">1</button>
+          <button type="button" class="key" data-key="2">2</button>
+          <button type="button" class="key" data-key="3">3</button>
+          <button type="button" class="key" data-key="4">4</button>
+          <button type="button" class="key" data-key="5">5</button>
+          <button type="button" class="key" data-key="6">6</button>
+          <button type="button" class="key" data-key="7">7</button>
+          <button type="button" class="key" data-key="8">8</button>
+          <button type="button" class="key" data-key="9">9</button>
+          <button type="button" class="key key-fn" data-key="back" aria-label="退格">⌫</button>
+          <button type="button" class="key" data-key="0">0</button>
+          <button type="button" class="key key-ok" data-key="ok" aria-label="确认完成">✓</button>
         </div>
 
         {{if .D.PickTail}}
@@ -136,7 +139,47 @@
         {{if .D.Tasks}}
         <ul class="task-list">
           {{range .D.Tasks}}
-          <li class="task{{if .Done}} done{{end}}{{if .Skipped}} skipped{{end}}{{if .Urgent}} urgent{{end}}" style="--asg:{{.AssigneeHex}}">
+          {{if or .Done .Skipped}}
+          <li class="task task-done" style="--asg:{{.AssigneeHex}}">
+            <details class="done-fold">
+              <summary>
+                <span class="ticket" style="--tag:{{.PackageColor}}"><b>{{.CustomerTail}}</b>{{.CustomerName}}</span>
+                <span class="pkg">{{.PackageName}}</span>
+                <span class="chip {{if .Done}}chip-active{{else}}chip-paused{{end}}">{{if .Done}}已完成{{else}}已跳过{{end}}</span>
+                {{if .Urgent}}<span class="tag-urgent">加急</span>{{end}}
+                <span class="fold-caret" aria-hidden="true"></span>
+              </summary>
+              <div class="done-detail">
+                <div class="task-meta">
+                  <span class="asg{{if .AssigneeNone}} none{{end}}"><i style="background:{{.AssigneeHex}}"></i>{{.AssigneeLabel}}</span>
+                  <span>{{.RemainText}}</span>
+                  {{if .DueText}}<span class="due due-{{.Eval.Level}}">{{.DueText}}</span>{{end}}
+                </div>
+                {{if .Note}}<div class="task-note">{{.Note}}{{if .Operator}} · {{.Operator}}{{end}}</div>{{end}}
+                <div class="task-actions">
+                  <form method="post" action="/checkins/{{.CheckinID}}/delete">
+                    <input type="hidden" name="back" value="{{$.D.Back}}">
+                    <button class="btn btn-sm btn-ghost" type="submit">撤销打卡</button>
+                  </form>
+                  <details class="more-actions">
+                    <summary class="btn btn-sm btn-ghost" title="更多操作" aria-label="更多操作">⋯</summary>
+                    <div class="more-menu">
+                      <form method="post" action="/tasks/urgent">
+                        <input type="hidden" name="sub_id" value="{{.ID}}">
+                        <input type="hidden" name="date" value="{{$.D.Selected}}">
+                        <input type="hidden" name="urgent" value="{{if .Urgent}}0{{else}}1{{end}}">
+                        <input type="hidden" name="back" value="{{$.D.Back}}">
+                        <button class="btn btn-sm {{if .Urgent}}btn-urgent{{else}}btn-ghost{{end}}" type="submit">{{if .Urgent}}取消加急{{else}}标记加急{{end}}</button>
+                      </form>
+                      <a class="btn btn-sm" href="/calendar?y={{$.D.Year}}&m={{$.D.Month}}&d={{$.D.Selected}}&pkg={{$.D.PkgID}}&extend={{.ID}}#extend">追加时长</a>
+                    </div>
+                  </details>
+                </div>
+              </div>
+            </details>
+          </li>
+          {{else}}
+          <li class="task{{if .Urgent}} urgent{{end}}" style="--asg:{{.AssigneeHex}}">
             <div class="task-main">
               <a class="task-title" href="/customers/{{.CustomerID}}">
                 <span class="ticket" style="--tag:{{.PackageColor}}"><b>{{.CustomerTail}}</b>{{.CustomerName}}</span>
@@ -151,32 +194,21 @@
               {{if .Note}}<div class="task-note">{{.Note}}{{if .Operator}} · {{.Operator}}{{end}}</div>{{end}}
             </div>
             <div class="task-actions">
-              {{if or .Done .Skipped}}
-              <span class="chip {{if .Done}}chip-active{{else}}chip-paused{{end}}">{{if .Done}}已完成{{else}}已跳过{{end}}</span>
-              {{else}}
               <form method="post" action="/subscriptions/{{.ID}}/checkin">
                 <input type="hidden" name="date" value="{{$.D.Selected}}">
                 <input type="hidden" name="status" value="done">
                 <input type="hidden" name="back" value="{{$.D.Back}}">
                 <button class="btn btn-sm btn-primary">完成</button>
               </form>
-              {{end}}
               <details class="more-actions">
                 <summary class="btn btn-sm btn-ghost" title="更多操作" aria-label="更多操作">⋯</summary>
                 <div class="more-menu">
-                  {{if or .Done .Skipped}}
-                  <form method="post" action="/checkins/{{.CheckinID}}/delete">
-                    <input type="hidden" name="back" value="{{$.D.Back}}">
-                    <button class="btn btn-sm btn-ghost" type="submit">撤销打卡</button>
-                  </form>
-                  {{else}}
                   <form method="post" action="/subscriptions/{{.ID}}/checkin">
                     <input type="hidden" name="date" value="{{$.D.Selected}}">
                     <input type="hidden" name="status" value="skipped">
                     <input type="hidden" name="back" value="{{$.D.Back}}">
                     <button class="btn btn-sm btn-ghost" type="submit">跳过这次</button>
                   </form>
-                  {{end}}
                   <form method="post" action="/tasks/urgent">
                     <input type="hidden" name="sub_id" value="{{.ID}}">
                     <input type="hidden" name="date" value="{{$.D.Selected}}">
@@ -190,6 +222,7 @@
             </div>
           </li>
           {{end}}
+          {{end}}
         </ul>
         {{else}}<p class="muted">这天没有待打任务。</p>{{end}}
       </section>