[client] clipboard: add transport provider interface

Route clipboard exchange through a provider interface. Connected
transports take priority while SPICE remains the fallback.

Track asynchronous X11 and Wayland transfers by request, preserving
clipboard ownership across provider changes.

Use PureSpice clipboard status notifications for capability and
lifecycle updates.

client/src/app.c

@@ -299,148 +299,31 @@ void app_handleEnterEvent(bool entered)
 
 void app_clipboardRelease(void)
 {
-  if (!g_params.clipboardToVM)
-    return;
-
-  purespice_clipboardRelease();
+  lgClipboard_release();
 }
 
 void app_clipboardNotifyTypes(const LG_ClipboardData types[], int count)
 {
-  if (!g_params.clipboardToVM)
+  if (count < 0)
     return;
-
-  if (count == 0)
-  {
-    purespice_clipboardRelease();
-    return;
-  }
-
-  PSDataType conv[count];
-  for(int i = 0; i < count; ++i)
-    conv[i] = cb_lgTypeToSpiceType(types[i]);
-
-  purespice_clipboardGrab(conv, count);
+  lgClipboard_notifyTypes(types, (size_t)count);
 }
 
-void app_clipboardNotifySize(const LG_ClipboardData type, size_t size)
+void app_clipboardData(LG_ClipboardRequest request,
+    const LG_ClipboardData type, const void * data, size_t size)
 {
-  if (!g_params.clipboardToVM)
-    return;
-
-  if (type == LG_CLIPBOARD_DATA_NONE)
-  {
-    purespice_clipboardRelease();
-    return;
-  }
-
-  const PSDataType spiceType = cb_lgTypeToSpiceType(type);
-  if (spiceType == SPICE_DATA_NONE)
-    return;
-
-  if (!purespice_clipboardDataStart(spiceType, size))
-  {
-    DEBUG_ERROR("Failed to start a %zu-byte SPICE clipboard transfer", size);
-    return;
-  }
-
-  g_state.cbWriteType = spiceType;
-  g_state.cbChunked   = true;
-  g_state.cbXfer      = size;
+  lgClipboard_data(request, type, data, size);
 }
 
-void app_clipboardData(const LG_ClipboardData type, uint8_t * data, size_t size)
+void app_clipboardAbort(LG_ClipboardRequest request)
 {
-  if (!g_params.clipboardToVM)
-    return;
-
-  const PSDataType spiceType = cb_lgTypeToSpiceType(type);
-  if (spiceType == SPICE_DATA_NONE)
-    return;
-
-  if (size && !data)
-  {
-    DEBUG_ERROR("SPICE clipboard data is NULL");
-    return;
-  }
-
-  if (g_state.cbChunked)
-  {
-    if (spiceType != g_state.cbWriteType)
-    {
-      DEBUG_ERROR("SPICE clipboard transfer type changed");
-      return;
-    }
-
-    if (size > g_state.cbXfer)
-    {
-      DEBUG_ERROR("SPICE clipboard chunk exceeds the remaining transfer size");
-      return;
-    }
-
-    if (size && !purespice_clipboardData(spiceType, data, size))
-    {
-      DEBUG_ERROR("Failed to send SPICE clipboard data");
-      return;
-    }
-
-    g_state.cbXfer -= size;
-    if (g_state.cbXfer == 0)
-    {
-      g_state.cbWriteType = SPICE_DATA_NONE;
-      g_state.cbChunked   = false;
-    }
-    return;
-  }
-
-  if (!purespice_clipboardDataStart(spiceType, size))
-  {
-    DEBUG_ERROR("Failed to start a %zu-byte SPICE clipboard transfer", size);
-    return;
-  }
-
-  if (size && !purespice_clipboardData(spiceType, data, size))
-    DEBUG_ERROR("Failed to send SPICE clipboard data");
+  lgClipboard_abort(request);
 }
 
-bool app_clipboardRequest(const LG_ClipboardReplyFn replyFn, void * opaque)
+bool app_clipboardRequest(LG_ClipboardData type,
+    LG_ClipboardReplyFn replyFn, void * opaque)
 {
-  if (!g_params.clipboardToLocal || !replyFn || !g_state.cbRequestList)
-    return false;
-
-  const PSDataType type = atomic_load_explicit(
-      &g_state.cbRemoteType, memory_order_acquire);
-  struct CBRequest * cbr = malloc(sizeof(*cbr));
-  if (!cbr)
-  {
-    DEBUG_ERROR("out of memory");
-    return false;
-  }
-
-  cbr->type    = type;
-  cbr->replyFn = replyFn;
-  cbr->opaque  = opaque;
-
-  if (!ll_push(g_state.cbRequestList, cbr))
-  {
-    free(cbr);
-    return false;
-  }
-
-  if (purespice_clipboardRequest(type))
-    return true;
-
-  /*
-   * Queue the callback before sending so a fast response cannot arrive before
-   * its request is visible. If another thread has already consumed it, the
-   * callback owns both cbr and opaque and the request completed successfully
-   * from the caller's perspective.
-   */
-  if (!ll_removeData(g_state.cbRequestList, cbr))
-    return true;
-
-  free(cbr);
-  return false;
+  return lgClipboard_request(type, replyFn, opaque);
 }
 
 static int mapSpiceToImGuiButton(uint32_t button)