feat: 视频分析抽帧功能及 UI 优化

- 新增 extractVideoFrames 前端视频抽帧，支持按时长自动调整采样率
- 视频帧以 detail:low 图像序列发送，兼容 GPT-5.5 等模型
- 对话记录仅显示首帧缩略图，隐藏抽帧细节保持界面简洁
- 视频预览增加时长标签显示
- 修复视频预览缩略图未等比显示的问题
- 调整模型列表顺序，移除冗余标注
- 移除后端 ChatProxy 调试打印
- 重启按钮绕过 beforeunload 弹窗

Co-Authored-By: Claude Opus 4.6 <[email protected]>

web/js/restartButton.js

@@ -56,14 +56,23 @@ app.registerExtension({
             const maxAttempts = 40;
             const interval = setInterval(async () => {
                 attempts++;
-                if (attempts > maxAttempts) { clearInterval(interval); location.reload(); return; }
+                if (attempts > maxAttempts) { clearInterval(interval); forceReload(); return; }
                 try {
                     const r = await fetch("/api/system_stats", { signal: AbortSignal.timeout(2000) });
-                    if (r.ok) { clearInterval(interval); location.reload(); }
+                    if (r.ok) { clearInterval(interval); forceReload(); }
                 } catch {}
             }, 1500);
         }
 
+        function forceReload() {
+            window.onbeforeunload = null;
+            Object.defineProperty(BeforeUnloadEvent.prototype, "returnValue", {
+                get() { return ""; },
+                set() {}
+            });
+            location.reload();
+        }
+
         const observer = new MutationObserver(inject);
         observer.observe(document.body, { childList: true, subtree: true });
         setTimeout(inject, 2000);