Feature: Web remote desktop bidirectional text clipboard sync

Add keyboard-shortcut (Ctrl+C / Ctrl+X / Ctrl+V) text clipboard transfer
between the browser and the remote desktop, reusing the clipboard protocol
that already exists in the native viewer (COMMAND_SCREEN_GET_CLIPBOARD=24,
COMMAND_SCREEN_SET_CLIPBOARD=25, TOKEN_CLIPBOARD_TEXT=118) so the client
needs no change.

Local -> remote: pressing Ctrl+V reads the browser clipboard, pushes it to
the remote clipboard (UTF-8 -> GBK, matching the client's CF_TEXT/ANSI
handling) and then synthesizes a remote Ctrl+V so the pasted text is the
newly delivered one.

Remote -> local: Ctrl+C or Ctrl+X is forwarded to the remote as usual and,
after a short delay, the remote clipboard is pulled back and written to the
browser clipboard for a later local Ctrl+V.

Both the MFC and Go servers get the same three clipboard signaling paths
(clipboard_set, clipboard_get, clipboard_text) so the shared single-page
frontend behaves identically on either backend.

Co-Authored-By: deepseek-v4-pro

server/web/index.html

@@ -1365,6 +1365,7 @@
     <script>
         let ws = null, token = null, decoder = null, devices = [], currentDevice = null;
         let frameCount = 0, lastFrameTime = 0, fps = 0, pingInterval = null;
+        let skipNextCtrlVKeyup = false;   // 剪贴板桥：抑制 pasteToRemote 合成的 Ctrl+V 物理 keyup
         // FPS 计数：原始风格——decoder.onOutput 里 ++，每经过 1 秒采样一次。
         // 简单直接，与本次会话改动前一致。
         // 网络流量统计：handleBinaryFrame 累加，每 1 秒钟 renderStats 读出
@@ -1863,6 +1864,12 @@
                         applyRemoteCursor(msg.index);
                     }
                     break;
+                case 'clipboard_text':
+                    // 远程剪贴板文本回传：写回浏览器（即本机）剪贴板
+                    if (msg.text) {
+                        try { navigator.clipboard.writeText(msg.text); } catch (e) {}
+                    }
+                    break;
                 case 'device_offline':
                     // Only handle if this is the device we're currently viewing
                     if (!token) break;
@@ -3714,6 +3721,28 @@
             }
         }
 
+        // 本地剪贴板 → 远程：读浏览器剪贴板，先 clipboard_set 到远程，再合成一次完整 Ctrl+V。
+        // 合成按键放在 readText 的 then 里，保证 clipboard_set 先于 Ctrl+V 到达（同一条 WS 有序）。
+        function pasteToRemote() {
+            const press = () => { sendKey(86, true, false); sendKey(86, false, false); };
+            navigator.clipboard.readText().then(function(text) {
+                if (text && ws && ws.readyState === WebSocket.OPEN && token) {
+                    ws.send(JSON.stringify({ cmd: 'clipboard_set', token, text }));
+                }
+                press();
+            }).catch(function() { press(); });  // 读剪贴板被拒/为空：仍执行一次普通远程粘贴
+        }
+
+        // 远程剪贴板 → 本地：等远程完成拷贝（启发式延时）后请求远程剪贴板，回包写回浏览器剪贴板。
+        // 不保证 100% 命中，失败用户二次 Ctrl+C 即可。
+        function scheduleCopyFromRemote() {
+            setTimeout(function() {
+                if (ws && ws.readyState === WebSocket.OPEN && token) {
+                    ws.send(JSON.stringify({ cmd: 'clipboard_get', token }));
+                }
+            }, 250);
+        }
+
         function showTouchIndicator(x, y) {
             touchIndicator.style.left = x + 'px';
             touchIndicator.style.top = y + 'px';
@@ -4198,14 +4227,38 @@
             // controlling the remote — see the F11 handler above. Skip here
             // to let that one handle it.
             if (e.key === 'F11' && !controlEnabled) return;
+
+            // 文本剪贴板桥（secure context 下 navigator.clipboard 可用）。
+            // Ctrl/Cmd+V：把本地剪贴板文本先灌到远程剪贴板，再合成一次 Ctrl+V 粘贴。
+            // Ctrl/Cmd+C / Ctrl/Cmd+X：照常转发给远程（远程完成拷贝/剪切），随后延迟拉取远程剪贴板回本地。
+            if (controlEnabled && (e.ctrlKey || e.metaKey) && !e.shiftKey && !e.altKey) {
+                if (e.keyCode === 86) {            // Ctrl/Cmd+V
+                    e.preventDefault();
+                    skipNextCtrlVKeyup = true;
+                    pasteToRemote();
+                    return;
+                }
+                // e.keyCode === 67(C)/88(X) 时落到下面的 sendKey 原样转发，转发后再延迟拉取
+            }
+
             e.preventDefault();
             sendKey(e.keyCode, true, e.altKey);
+
+            if (controlEnabled && (e.ctrlKey || e.metaKey) && !e.shiftKey && !e.altKey && (e.keyCode === 67 || e.keyCode === 88)) {
+                scheduleCopyFromRemote();
+            }
         });
 
         document.addEventListener('keyup', function(e) {
             if (!document.getElementById('screen-page').classList.contains('active')) return;
             if (e.target.tagName === 'INPUT') return;
             if (e.key === 'F11' && !controlEnabled) return;
+            // 由 pasteToRemote 合成的完整 Ctrl+V 按下：物理 keyup 不再转发，避免 down/up 乱序
+            if (e.keyCode === 86 && skipNextCtrlVKeyup) {
+                skipNextCtrlVKeyup = false;
+                e.preventDefault();
+                return;
+            }
             e.preventDefault();
             sendKey(e.keyCode, false, e.altKey);
         });