Atlas sheet starter

This is a small Chrome extension for sheet authors. Chrome and Arc can load it.
You can use and change this sample under the MIT license in LICENSE.txt.

1. Save all six files in one folder: manifest.json, background.js, atlas.js,
   sheet.js, README.txt and LICENSE.txt.
2. Replace https://sheets.example.com in manifest.json and background.js with
   your sheet's origin. An origin is the protocol and host, for example
   https://sheets.your-game.com. Keep the /* suffix in the manifest match.
3. Change 'my-sheet' in sheet.js to a short name for your service.
4. Add a button to your sheet:

   <button data-atlas-roll="d8+3" data-atlas-character="Mira"
     data-atlas-name="Spear damage">Roll in Atlas</button>

   Update these values when the character changes. Include all bonuses.
   You can also change sheet.js to read your own sheet controls.
5. Open chrome://extensions. Turn on Developer mode. Click Load unpacked.
   Choose this folder. In Arc, use arc://extensions.
6. Reload your sheet tab and your Atlas player tab. Join a table where the GM
   is connected and a scene is showing. Keep one Atlas player tab open.
7. Click Roll in Atlas on your sheet. Check the result and label in Atlas.

The starter needs no build tool, account key or table code. It detects the
single open Atlas tab. It refuses to send when more than one is open.
It never repeats a failed or timed-out roll. Check the table log if delivery
is uncertain. A successful send means the request went to the GM; it does
not confirm a result. The GM still checks the request.

Only clicks on the declared sheet origin enter the starter. It accepts no
cross-origin window messages. Do not add <all_urls>, externally_connectable,
credential access or direct relay calls for a sheet integration.

API guide: https://atlas-vtt.dev/docs/reference/sheet-roll-api
