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/js/app.js

@@ -172,20 +172,47 @@ async function loadPluginPage(pluginName) {
 }
 
 
-// ═══ Global file/dir picker (reusable by any page) ═══
-// Usage: pickPath('dir', function(path) { document.getElementById('my-input').value = path; })
+// ═══ Global file/dir picker (in-page iframe modal) ═══
 window.pickPath = function(mode, callback) {
   var id = 'picker_' + Date.now();
-  window['_pickCallback_' + id] = callback;
   var url = './static/pages/files.html?picker=1&mode=' + (mode || 'dir') + '&cb=' + id;
-  var w = window.open(url, 'fm-picker', 'width=680,height=520');
-  if (!w) { alert('请允许弹窗以使用文件选择器'); return; }
-  // Listen for pick result
+
+  // Create modal overlay
+  var overlay = document.createElement('div');
+  overlay.id = 'fm-picker-overlay';
+  overlay.style.cssText = 'position:fixed;inset:0;z-index:500;background:rgba(0,0,0,.5);display:flex;align-items:center;justify-content:center';
+  overlay.onclick = function(e) { if (e.target === overlay) closePicker(); };
+
+  var box = document.createElement('div');
+  box.style.cssText = 'background:var(--md-sys-color-surface-container-high);border-radius:var(--shape-lg);width:720px;height:520px;max-width:95vw;max-height:85vh;display:flex;flex-direction:column;overflow:hidden;box-shadow:var(--md-sys-elevation-5)';
+
+  // Header
+  var header = document.createElement('div');
+  header.style.cssText = 'display:flex;justify-content:space-between;align-items:center;padding:12px 16px;border-bottom:1px solid var(--outline);flex-shrink:0';
+  header.innerHTML = '<span style="font-weight:500;color:var(--primary)">📂 选择' + (mode==='file'?'文件':'目录') + '</span>' +
+    '<button class="btn btn-sm btn-outlined" onclick="closePicker()" style="font-size:16px;line-height:1">✕</button>';
+  box.appendChild(header);
+
+  // Iframe
+  var iframe = document.createElement('iframe');
+  iframe.src = url;
+  iframe.style.cssText = 'flex:1;border:none;width:100%';
+  box.appendChild(iframe);
+  overlay.appendChild(box);
+  document.body.appendChild(overlay);
+
+  function closePicker() {
+    window.removeEventListener('message', handler);
+    if (overlay.parentNode) overlay.parentNode.removeChild(overlay);
+  }
+  window._closePicker = closePicker;
+
+  // Listen for pick result from iframe
   window.addEventListener('message', function handler(e) {
     try {
       var d = JSON.parse(e.data);
       if (d.action === 'fm-picked' && d.callback_id === id) {
-        window.removeEventListener('message', handler);
+        closePicker();
         if (d.path && callback) callback(d.path);
       }
     } catch(ex) {}