feat: add 创建排课 button to calendar; fix 操作记录 spacing

- Add "创建排课" custom button in FullCalendar header toolbar, defaults
  to current date/time + 45min duration, guarded by is_teacher check
- Add margin-bottom to 操作记录 cell so it doesn't crowd the footer buttons

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/pages/clazz/index.vue

@@ -98,7 +98,7 @@
             <van-tag :closeable="false" type="primary" @click="gotoDaka(daka.id)" v-for="daka in store.current.dakas.vals">{{daka.name}}</van-tag>
           </div>
           <van-calendar v-model:show="state.showCalendar" :min-date="repeatMinDate" :default-date="repeatDefaultDate" @confirm="onChangeDate" type="range" color="#1989fa" />
-          <van-cell title="操作记录" is-link v-if="state.readonly && store.current.id" @click="showAuditLogPopup" />
+          <van-cell title="操作记录" is-link v-if="state.readonly && store.current.id" @click="showAuditLogPopup" style="margin-bottom: 0.2rem;" />
         </div>
         <div class="footer" v-if="is_creator || !store.current.id ">
           <template v-if="state.readonly">
@@ -462,12 +462,25 @@ export default defineComponent({
           click: function() {
             calendar.value.getApi().gotoDate(new Date())
           }
+        },
+        createClazz: {
+          text: '创建排课',
+          click: function() {
+            if (!is_teacher.value) return;
+            const now = new Date();
+            store.current.start_from = formatDate(now, DateFormatter.DateTimeSave);
+            now.setMinutes(now.getMinutes() + 45);
+            store.current.end_by = formatDate(now, DateFormatter.DateTimeSave);
+            state.editing = true;
+            state.readonly = false;
+            state.title = "新增排课"
+          }
         }
       },
       headerToolbar: {
         left: 'prev,current,next',
         center: 'title',
-        right: ''
+        right: 'createClazz'
       },
       plugins: [ dayGridPlugin, bootstrap5Plugin, timeGridPlugin, interactionPlugin ],
       initialView: 'timeGridWeek',