Count as queued only what a scan will download on its own (#113)

Every file in state 'pending' counted as waiting to download: 4420 in production, across 12
shows. Since #97 a scan only downloads among a feed's newest max_new_per_check items, so those
were back-catalogue episodes no scan would take; the real queue was 0.

A new state, 'held': listed and downloadable by hand, but outside the feed's newest items, or of
a feed nothing downloads automatically. Db::hold_back moves a feed's waiting files between
'pending' and 'held' each time the feed is due, changed or not, and again after its items are
stored, so a new episode, a raised limit or auto-download turned on or off moves them. A held
file keeps its item's place among the newest, as a downloaded one does. 'pending' now means
queued, so ipx status, /api/status and the dashboard read true without changing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/items.ts

@@ -328,7 +328,7 @@ function encBox(x){
   // Nothing on disk. For an image or a PDF you usually just want to look at it, so link
   // straight to the publisher's copy in a new tab -- no download, and nothing proxied
   // through here, which would make ipx a fetch-anything relay.
-  const viewable = !isPlayable(x) && x.state !== 'pending';
+  const viewable = !isPlayable(x) && x.state !== 'pending' && x.state !== 'held';
   return `<div class="encbox">
     ${kindIcon(x)}
     <span class="meta" style="flex:1">${size}</span>