feat: AI 周报摘要提示词自定义设置

- system_config 新增 ai_summary_prompt 配置键
- generate_summary 从数据库加载自定义提示词，为空则使用默认 SUMMARY_SYSTEM_PROMPT
- 系统设置新增「AI 周报提示词」卡片，支持编辑和清空恢复默认

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

frontend/src/views/desktop/Settings.vue

@@ -18,6 +18,8 @@ const notificationTimeLoading = ref(false)
 const holidays = ref('')
 const holidaysLoading = ref(false)
 const holidaysRefreshing = ref(false)
+const aiPrompt = ref('')
+const aiPromptLoading = ref(false)
 
 const importLoading = ref(false)
 const importFile = ref<File | null>(null)
@@ -38,6 +40,9 @@ onMounted(async () => {
     if (res.data?.holidays) {
       holidays.value = res.data.holidays
     }
+    if (res.data?.ai_summary_prompt) {
+      aiPrompt.value = res.data.ai_summary_prompt
+    }
   } catch (_) {}
 })
 
@@ -91,6 +96,16 @@ async function handleSaveHolidays() {
   } finally { holidaysLoading.value = false }
 }
 
+async function handleSaveAiPrompt() {
+  aiPromptLoading.value = true
+  try {
+    await api.put('/system-config/ai_summary_prompt', { value: aiPrompt.value })
+    ElMessage.success(aiPrompt.value.trim() ? 'AI 提示词已保存' : '已恢复默认提示词')
+  } catch (e: any) {
+    ElMessage.error(e.response?.data?.detail || '保存失败')
+  } finally { aiPromptLoading.value = false }
+}
+
 async function handleRefreshHolidays() {
   holidaysRefreshing.value = true
   try {
@@ -268,6 +283,36 @@ async function handleImportPreview() {
       </div>
     </el-card>
 
+    <!-- AI Summary Prompt -->
+    <el-card class="setting-card">
+      <template #header>
+        <div class="card-header-title">
+          <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" style="margin-right:6px; color: var(--gold)">
+            <polygon points="13 2 3 14 12 14 11 22 21 10 12 10 13 2"></polygon>
+          </svg>
+          AI 周报提示词
+        </div>
+      </template>
+      <div class="setting-row">
+        <div class="setting-col" style="flex:1">
+          <label class="setting-label">自定义 System Prompt（清空则使用默认提示词）</label>
+          <div style="display:flex;gap:8px;align-items:flex-start">
+            <el-input
+              v-model="aiPrompt"
+              type="textarea"
+              :rows="6"
+              placeholder="留空使用默认提示词，输入自定义内容将替换默认提示词..."
+              style="flex:1"
+            />
+            <el-button type="primary" :loading="aiPromptLoading" @click="handleSaveAiPrompt" size="small">保存</el-button>
+          </div>
+          <p style="color:var(--warm-gray);font-size:12px;margin-top:6px">
+            自定义 AI 生成周报摘要时的行为风格。支持 Markdown 格式约束。留空则恢复默认提示词。
+          </p>
+        </div>
+      </div>
+    </el-card>
+
     <!-- Import -->
     <el-card class="setting-card">
       <template #header>