Add Twitch extension listing assets (icon, discovery image, screenshot)

assets/twitch-listing/README.md

@@ -0,0 +1,26 @@
+# Twitch extension listing assets
+
+Images for the extension's listing in the Twitch developer console (the "Assets" / listing step; see the
+submission checklist in [`extension/README.md`](../../extension/README.md)). They are deliberately outside
+`extension/` so they are never part of the uploaded extension zip.
+
+| File | Size | Console field |
+|---|---|---|
+| `extension-icon-100x100.png` | 100 x 100 | Extension icon |
+| `discovery-image-300x200.png` | 300 x 200 | Discovery image |
+| `screenshot-1024x768.png` | 1024 x 768 | Screenshot |
+
+Sizes follow Twitch's listing requirements as last checked; confirm them in the console when uploading
+(verify in console), since Twitch changes these occasionally.
+
+## Notes
+
+- **Icon and discovery image** use the EDNexus mark and the brand palette from the design system
+  (`extension/css/tokens.css`). The icon is an opaque square; Twitch applies its own rounding.
+- **Screenshot** is the real overlay (`extension/video_overlay.html`) rendered in its local mock mode
+  (`?mock=1`, see `extension/README.md`) with the bundled sample payload, panel opened, over an illustrative
+  space backdrop standing in for a stream. The commander shown ("Vega") is fictional sample data. Twitch
+  reviewers may prefer a screenshot taken from a real test channel while the desktop app publishes (developer
+  mode can drive the card); replace this file if so.
+- Re-generate the screenshot by serving `extension/` locally, opening
+  `http://127.0.0.1:8931/video_overlay.html?mock=1` in a 1024 x 768 window and opening the panel.