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/go/web/ws_handlers.go

@@ -8,6 +8,7 @@ import (
 	"github.com/yuanyuanxiang/SimpleRemoter/server/go/hub"
 	"github.com/yuanyuanxiang/SimpleRemoter/server/go/protocol"
 	"github.com/yuanyuanxiang/SimpleRemoter/server/go/wsauth"
+	"golang.org/x/text/encoding/simplifiedchinese"
 )
 
 // rotateChallenge replaces the client's nonce with a fresh one and pushes a
@@ -64,6 +65,10 @@ func (h *wsHub) dispatch(c *wsClient, cmd string, raw []byte) {
 		h.handleMouse(c, raw)
 	case "key":
 		h.handleKey(c, raw)
+	case "clipboard_set":
+		h.handleClipboardSet(c, raw)
+	case "clipboard_get":
+		h.handleClipboardGet(c, raw)
 	case "term_open":
 		h.handleTermOpen(c, raw)
 	case "term_input":
@@ -559,6 +564,59 @@ func (h *wsHub) handleKey(c *wsClient, raw []byte) {
 	_ = h.devices.SendToScreen(deviceID, pkt)
 }
 
+// handleClipboardSet relays the browser's local clipboard text into the remote
+// device's clipboard via COMMAND_SCREEN_SET_CLIPBOARD (25). The client's
+// UpdateClientClipboard stores the payload as CF_TEXT (ANSI/GBK), so we encode
+// the UTF-8 input to GBK here — matching the C++ WebService (explicit code
+// page 936) and the existing MCP remote_clipboard convention. Non-GBK glyphs
+// (emoji, some accented Latin) collapse to '?' — an accepted limitation.
+func (h *wsHub) handleClipboardSet(c *wsClient, raw []byte) {
+	if !h.requireAuth(c, raw, "clipboard_set_result") {
+		return
+	}
+	var in struct {
+		Text string `json:"text"`
+	}
+	if err := json.Unmarshal(raw, &in); err != nil {
+		return
+	}
+	if in.Text == "" {
+		return
+	}
+	deviceID := c.watching
+	if deviceID == "" {
+		return
+	}
+	gbk, err := simplifiedchinese.GBK.NewEncoder().Bytes([]byte(in.Text))
+	if err != nil {
+		h.log.Warn("clipboard_set: GBK encode failed: %v", err)
+		return
+	}
+	payload := append([]byte{protocol.CommandScreenSetClipboard}, gbk...)
+	if err := h.devices.SendToScreen(deviceID, payload); err != nil {
+		h.log.Warn("clipboard_set: device=%s: %v", deviceID, err)
+		return
+	}
+	h.log.Info("clipboard_set sent: device=%s len=%d", deviceID, len(gbk))
+}
+
+// handleClipboardGet asks the remote device for its clipboard text via
+// COMMAND_SCREEN_GET_CLIPBOARD (24, a single byte). The device replies with
+// TOKEN_CLIPBOARD_TEXT, which the hub relays back to the browser.
+func (h *wsHub) handleClipboardGet(c *wsClient, raw []byte) {
+	if !h.requireAuth(c, raw, "clipboard_get_result") {
+		return
+	}
+	deviceID := c.watching
+	if deviceID == "" {
+		return
+	}
+	if err := h.devices.SendToScreen(deviceID, []byte{protocol.CommandScreenGetClipboard}); err != nil {
+		h.log.Warn("clipboard_get: device=%s: %v", deviceID, err)
+		return
+	}
+}
+
 // handleCreateUser provisions a new web account. Admin-only. Mirrors the
 // C++ CWebService::HandleCreateUser semantics (WebService.cpp:1009): the
 // password is hashed with a fresh salt, the user table is persisted, and