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

docs/architecture.md

@@ -104,7 +104,7 @@ else a `401`.
 | `GET /login`, `POST /api/login`, `POST /api/logout`, `GET /api/me` | sign-in |
 | `GET /api/feeds`, `POST /api/feeds` | your subscriptions; subscribe |
 | `PATCH /api/feeds/{id}`, `DELETE /api/feeds/{id}` | your settings or (admin) the feed's; unsubscribe |
-| `GET /api/feeds/{id}/entries` | paged, filtered, searchable |
+| `GET /api/feeds/{id}/entries` | paged, filtered, searchable, sortable (`sort` = kept, title, feed, type, size or published; `dir` = asc or desc) |
 | `GET /api/entries` | the same, across every feed you subscribe to (All Subscriptions) |
 | `POST /api/feeds/{id}/read-all`, `POST /api/feeds/{id}/download-latest` | |
 | `POST /api/read-all` | everything read in every feed you subscribe to (All Subscriptions) |