dsh-wait: Add confirmation to message sending in DSH Web UI

dsh-wait is a DSH client plugin maintained by A-2788553793. It displays a confirmation window before sending messages in the Web UI, intercepting three methods: the Enter key, Ctrl/Cmd+Enter, and the Send button. If cancelled, the draft is retained. The dialog defaults focus to the Send button and supports Esc, clicking the overlay, and Tab navigation for cancellation. It supports truncating previews for text exceeding 4000 characters, does not intercept slash commands, and requires confirmation for new sessions and queued messages. If the plugin fails to load, sending is not blocked. It is installed via `plugin_manager` as a bundle, version 0.1.3, under the MIT license. The plugin is implemented using `document` capture listeners and depends on the host DOM structure. It shares the same permissions as the current DSH process; source code and license should be checked before installation.