fix: tui local shell consent UX (#1463)

- add local shell runner + denial notice + tests
- docs: describe ! local shell usage
- lint: drop unused Slack upload contentType
- cleanup: remove stray Swabble pins

Thanks @vignesh07.
Co-authored-by: Vignesh Natarajan <vigneshnatarajan92@gmail.com>

src/slack/send.ts

@@ -88,7 +88,7 @@ async function uploadSlackFile(params: {
   threadTs?: string;
   maxBytes?: number;
 }): Promise<string> {
-  const { buffer, contentType, fileName } = await loadWebMedia(params.mediaUrl, params.maxBytes);
+  const { buffer, fileName } = await loadWebMedia(params.mediaUrl, params.maxBytes);
   const basePayload = {
     channel_id: params.channelId,
     file: buffer,