新增搜索结果缓存功能

- 新增 search_cache 数据库表存储搜索缓存
- 搜索前优先查询缓存，命中则直接返回
- 缓存默认有效期7天，可配置
- 前端支持'使用缓存'开关选项
- 显示缓存状态提示
- 支持自动清理过期缓存

static/js/search.js

@@ -23,6 +23,7 @@ async function doSearch() {
     const keyword = document.getElementById('search-keyword').value.trim();
     const maxResults = parseInt(document.getElementById('search-count').value) || 10;
     const engine = document.getElementById('search-engine').value;
+    const useCache = document.getElementById('use-cache').checked;
     const autoFetch = document.getElementById('auto-fetch').checked;
     const autoSave = document.getElementById('auto-save').checked;
 
@@ -51,7 +52,7 @@ async function doSearch() {
         const response = await fetch(`${API_BASE}/api/articles/internet-search`, {
             method: 'POST',
             headers: { 'Content-Type': 'application/json' },
-            body: JSON.stringify({ keyword, max_results: maxResults, engine })
+            body: JSON.stringify({ keyword, max_results: maxResults, engine, use_cache: useCache })
         });
 
         const data = await response.json();
@@ -65,7 +66,15 @@ async function doSearch() {
             }));
 
             displayResults();
-            updateStatus('success', `找到 ${searchResults.length} 条结果`);
+            
+            // 显示缓存状态
+            if (data.cached) {
+                updateStatus('success', `找到 ${searchResults.length} 条结果（使用缓存）`);
+                showToast('使用缓存结果', 'success');
+            } else {
+                updateStatus('success', `找到 ${searchResults.length} 条结果`);
+            }
+            
             document.getElementById('results-count').textContent = `${searchResults.length} 条结果`;
             document.getElementById('save-all-btn').disabled = searchResults.length === 0;