feat: bChannel plugin for channel pings

[deployor]

lets people who dont have permission still send @channel / @here from the normal composer. works with images too. requires the bchannel slack app.

[Copilot]

Pull request overview

Adds a new Slick plugin (bChannel) that intercepts Slack message sending to enable @channel / @here broadcasts (and image attachments) via a required external “bChannel” Slack app + service, including a document-start preload hook for early network interception.

Changes:

• Introduces a large renderer-side integration that hooks fetch/XMLHttpRequest and Slack’s message composer pipeline to stage intents, upload images, and dispatch /bchannel when broadcasts are detected or denied.
• Registers a document-start preload script (Electron session preload) and adds settings + CSS for an in-app error dialog.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
plugins/bChannel/renderer.js	Implements Slack network/composer interception, bChannel handoff logic, attachment handling, and error dialog UI.
plugins/bChannel/index.js	Adds plugin entrypoint, settings, preload registration, and dialog CSS.

Suppressed comments (2)

plugins/bChannel/renderer.js:928

• The Escape key listener is only removed when Escape is pressed. If the dialog is closed via the close button, Cancel, or clicking the backdrop, the keydown handler remains registered, which can leak listeners and cause unexpected behavior on subsequent dialogs. Remove the keydown listener in the shared close handler.

    const closeDialog = () => removeDialog();
    close.addEventListener('click', closeDialog);
    dismiss.addEventListener('click', closeDialog);

plugins/bChannel/renderer.js:526

• Same as above: this error message implies all image types are supported, but IMAGE_TYPES only allows JPEG/PNG/GIF/WebP. Clarify the supported image types so users don’t get confused when attaching other image formats.

      if (!IMAGE_TYPES.has(mimeType)) {
        throw new Error('bChannel can only send image attachments. Remove the other files and try again.');
      }

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