dsh-prompt-spark: One-click draft rewriting in DSH input box

The dsh-prompt-spark, maintained by mihoojj, implements a 'sparkle' button next to the input toolbar for draft rewriting: Clicking uses the current session's model routing to rewrite the draft, replacing the input box content; as long as the text remains unedited, the button changes to 'undo' for immediate reversal. Long-pressing or right-clicking cycles through four fixed style presets (Clearer / Shorter / More formal / More casual). If text is selected before clicking, only the selected segment is rewritten, with surrounding text used as context. The control is hidden when the draft is empty or during submission. On failure, the draft is not modified, and the tooltip displays the error code. Installation requires only the package name `dsh-prompt-spark`; there are no settings pages or configuration files. The host and browser components are split into separate files, and modifications to the host side require restarting the application. The entire content is verified against the GitHub README and is released under the MIT license.