Feat: Per-client TLS transport toggle (TLS column + remote enable/disable)

Add a per-client TLS transport toggle controlled from the server, using the
presence of the client's trust-anchor certificate in the registry as the
single source of truth (no separate tls_enable flag).

- Client reports its TLS status via a new RES_TLS token (cert present -> 1)
  appended to LOGIN_INFOR's reserved field.
- Server online list gains a "TLS" column after the permission column.
- The "experimental features" right-click menu gains "TLS传输" / "取消TLS"
  with confirmation and a guard that prompts (instead of sending) when the
  server has no TLS certificate ready.
- New COMMAND_TLS_ENABLE / COMMAND_TLS_DISABLE (166/167): the server pushes
  its cert PEM into the client registry settings\tls_cert (enable) or deletes
  it (disable). The client picks this up on next startup via the existing
  ReadTrustAnchor logic, so the switch is non-live by design.
- Icons and en_US/zh_TW/de_DE translations for the new menu items.

Co-Authored-By: deepseek-v4-pro

server/2015Remote/context.h

@@ -22,6 +22,7 @@ enum {
     ONLINELIST_STARTTIME,
     ONLINELIST_CAPABILITIES,    // 客户端能力位
     ONLINELIST_PRIVILEGE,       // 权限级别 (SYSTEM/Admin/User)
+    ONLINELIST_TLS,             // TLS 传输启用标志 (0/1)
     ONLINELIST_MAX,
 };