A download limit means a show's newest episodes, not a pace (#97)

pending() took the newest files still pending, up to the limit, so once a show's latest three
were down, each full read of its feed took the three before them, working back through its
whole history. In production 4420 files (about 310 GB) were queued this way across 12 shows,
all on the default limit of 3, which is meant as "the latest three". It now takes only from the
feed's newest `limit` items with a file. 0, unlimited, still takes the whole back catalogue:
that is how the shows kept as an archive are set, along with limits of 100 and 10000.

The settings' wording followed the old behaviour ("The rest wait for the next scan"); the field
is now "Newest episodes to download", and says what 0 does.

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

web/src/dialogs.ts

@@ -275,10 +275,10 @@ function settingsModal(f, newUrl?: string){
       <span class="hint">Comma separated words or phrases. An item with one in its title or text
       is hidden from you and not downloaded for you, as well as those your Settings hide
       everywhere.</span></div>`}
-    <div class="field"><label>Max new downloads per scan</label>
+    <div class="field"><label>Newest episodes to download</label>
       <input type="number" id="smax" min="0" value="${f.max_new_per_check??''}">
-      <span class="hint">Blank follows the global default (${globalMax}). The rest wait for
-      the next scan.</span></div>
+      <span class="hint">Blank follows the global default (${globalMax}). Older episodes stay
+      listed to download by hand. <b>0 means every episode</b>, the whole back catalogue.</span></div>
     <label class="check"><input type="checkbox" id="sauto" ${f.auto_download?'checked':''}> Download new items automatically</label>
     <label class="check"><input type="checkbox" id="sexp" ${f.allow_explicit?'checked':''}> Allow items marked explicit</label>
     <div class="field"><label>Feed URL</label>