Feature: Add MCP (Model Context Protocol) server integration

Add an optional MCP server (JSON-RPC 2.0 over Streamable HTTP) exposing
an online-host listing tool, protected by a Bearer token. Disabled by
default; configured via a new "Extensions > MCP Settings" dialog.

- McpServer: httplib + JSON-RPC 2.0 dispatch (initialize/ping/tools/list/tools/call)
- McpSettingsDlg: runtime-created dialog for enable/port/bind/token
- HostJson: extract single-host JSON serialization shared with WebService
- FRP: expose MCP port (union with listening/Web ports) when bound to 0.0.0.0
- i18n: en_US / zh_TW translations

Co-Authored-By: deepseek-v4-pro

server/2015Remote/FeatureFlags.h

@@ -88,7 +88,9 @@ typedef struct FeatureFlags {
 #define MF_MASTER_TRAIL       (1ULL << 41)  // HIDE_MENU_MASTER_TRAIL
 #define MF_REQUEST_AUTH       (1ULL << 42)  // HIDE_MENU_REQUEST_AUTH
 
-// [43-63] Reserved
+#define MF_MCP_SETTINGS       (1ULL << 43)  // HIDE_MENU_MCP_SETTINGS
+
+// [44-63] Reserved
 
 
 // ============================================================