Sortable item table, Size in its own column, Subscribed as an icon

- Every column heading sorts (kept, title, feed, file type, size,
  published); a second click reverses it. The server sorts through a
  fixed whitelist (order_sql), so it covers the whole list, not the
  fifty loaded; the choice is remembered in the browser.
- Size is its own column and shows KB for small files instead of
  "0 MB". The Item heading is Title.
- Popular/Directory/Add feed: Subscribed is a green circle-check.
- Tests: every sort column runs and orders both ways (db); the table
  sorts by title both ways and remembers across a reload (browser).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0173mGu6rK18Ne7UGTwAaVJV

CHANGELOG.md

@@ -24,6 +24,9 @@ The long form, with what was wrong before and how it was found, is in
   and a status bar with the totals.
 - Mark everything read from All Subscriptions, across every feed you subscribe to
   (`POST /api/read-all`). It asks first. All Subscriptions can also check every feed from its header.
+- Click a column heading in the item table to sort by it (kept, title, feed, file type, size,
+  published); click again to reverse. The server sorts, so it covers the whole list, not just the
+  fifty shown, and the choice is remembered.
 
 ### Changed
 
@@ -45,10 +48,13 @@ The long form, with what was wrong before and how it was found, is in
   and read as closing the page. The remaining word buttons are icons too:
   - Log, Add feed, Users, Unsubscribe and OPML.
   - Popular's Subscribe, Copy and Sign out.
+  - The Subscribed label in Popular, the Directory and Add feed, which is now a green check.
   - The player's back, play, forward and close, which were font characters, and the folder arrow.
 - The toolbar's read and keep buttons show the selected item's state, with the same icons as the
   item's own buttons. Play, read and keep sit together, and Scan sits with add and unsubscribe.
 - An OPML subscription's page has the same header as a feed's, with its buttons in the same places.
+- The item table's size has its own column, apart from the file's type, and shows KB for small
+  files instead of "0 MB". The Item heading is now Title.
 - A file's type is an icon (audio, video, image, PDF, torrent, other), green once it is
   downloaded and red when the download failed, with the details in its tooltip. One icon per
   row keeps the column lined up. The DOWNLOADED and PENDING labels are gone.