docs: regenerate screenshots via the mock backend, add the channel page (#30)

Recapture every screen through the branch-only mock backend
(tools/screenshot-mock) so the app runs unmodified against real CC/Blender
content: the rows no longer repeat thumbnails (Continue watching, New local
videos and My videos draw different slices), the account has an avatar, the
player sits on a frame with something happening, and the Subscribe button reads
correctly. Adds a channel-page screenshot (banner, stats, Subscribe, full video
grid) and references it in the README.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -56,13 +56,19 @@ anything that isn't public.
 </p>
 
 **Channels.** One row per owner, with video, subscriber and play counts on
-every card. Open a channel for its banner, its stats and all its videos — and a
+every card.
-Subscribe button you can reach with the remote.
 
 <p align="center">
   <img src="docs/screenshots/channels.png" width="800" alt="Channels screen with channel cards" />
 </p>
 
+Open a channel for its banner, its stats and all its videos — with a Subscribe
+button you can reach with the remote.
+
+<p align="center">
+  <img src="docs/screenshots/channel.png" width="800" alt="A channel page: banner, stats, Subscribe button and the channel's videos" />
+</p>
+
 **The player** speaks remote: play and pause, seek back and forward, a seek bar
 with position and duration, and the video's info, comments and playlists a
 button away. Watching is reported to the server every 20 seconds, so where you