Terminal reader: play with mpv, mark read on move, folders and pins (#439, #440, #441)

p hands the item's downloaded file (/media/{id}) to mpv in its own window, with the token as a
header. Moving onto an item with j or k marks it read, as selecting one on the page does. The
feed list follows the page's order: pinned first, a subscribed OPML a folder that Space opens,
its unread the sum of its feeds', and P pins or unpins. scripts/build-tui.sh cross-builds the
binary for Linux and macOS under the same cap as the image builds.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RqkrVARreS9wxzH5o2rF7N

crates/tui/CHANGELOG.md

@@ -12,3 +12,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - `ipx`, iPX's reader in a terminal: your feeds, a feed's items and an item's text, read and flagged as on the page, signed in with an API token (#437).
+- `p` plays the item's file in mpv (#439).
+- Moving onto an item with `j` or `k` marks it read, as on the page (#441).
+- Feeds are listed as on the page: a subscribed OPML is a folder `Space` opens, and pinned feeds are at the top; `P` pins and unpins (#440).