fix: 文件选择器改为页内iframe弹窗 + 乱码编码修复 + API路径修复

- pickPath()从window.open改为页内iframe模态弹窗(遮罩+关闭按钮)
- files.html添加meta charset+CSS link,独立模式自动加载files.js
- API路径统一通过_apiUrl()构建,适配主面板和iframe两种上下文
- 独立iframe模式注入body/container覆写样式(无topbar)
- 选择模式栏移至底部margin-top:auto紧凑排列
- MD3风格toggle开关(显示隐藏复选框)
- CSS版本号缓存破坏

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

static/web_panel/pages/files.html

@@ -1,4 +1,6 @@
 <!-- File Manager Page -->
+<meta charset="UTF-8">
+<link rel="stylesheet" href="../css/style.css?v=0601">
 <div class="fm-container">
     <!-- Top bar: editable path + actions -->
     <div class="fm-toolbar">
@@ -64,3 +66,29 @@
         <div class="fm-context-item danger" onclick="FilesModule.ctxDelete()">🗑 删除</div>
     </div>
 </div>
+
+<script>
+// Load files.js for standalone mode (iframe picker)
+(function(){
+    // Reset body/container for iframe — no topbar, no sidebar
+    if(window.parent !== window){
+        var s=document.createElement('style');
+        s.textContent='html,body{height:100%;margin:0;overflow:hidden}.fm-container{height:100%;gap:8px}.fm-list{padding-bottom:0}';
+        document.head.appendChild(s);
+    }
+    var cssHref = document.querySelector('link[href*=\"style.css\"]')?.href || '';
+    // e.g. http://host:4200/SenSu/static/css/style.css → staticBase = .../SenSu/static
+    var staticBase = cssHref.replace(/\/css\/style\.css.*$/, '');
+    // apiBase = .../SenSu (strip /static)
+    var apiBase = cssHref.replace(/\/static\/css\/style\.css.*$/, '');
+    var script = document.createElement('script');
+    script.src = staticBase + '/pages/files.js?v=0602';
+    script.onload = function(){
+        if(window.FilesModule){
+            window.FilesModule._apiBase = apiBase;
+            if(window.FilesModule.init) window.FilesModule.init();
+        }
+    };
+    document.head.appendChild(script);
+})();
+</script>