Give the search a zero-result state, hide the strip while filtering

The client filter only toggles card.hidden, so a query matching nothing left
the list area blank while the unfiltered "Continue reading" strip stayed
populated above it — the screen contradicted itself and read as a crash.

list.html now carries a hidden no-match block; applyFilter counts visible cards,
fills the query in with textContent, and hides .recent for the duration of a
filter. The Clear-search button is handled by a delegated click listener so it
survives an htmx tab swap.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/templates/list.html

@@ -1,6 +1,13 @@
 {{define "list"}}
 {{if .Items}}
   {{range .Items}}{{template "card" .}}{{end}}
+  {{/* The client filter only hides cards, so without this the list area goes
+       blank on a query that matches nothing. filter.js fills in the query and
+       unhides it; it lives inside #list so a tab swap re-creates it. */}}
+  <div class="empty" id="no-match" hidden>
+    <strong>No titles match “<span class="no-match-q"></span>”.</strong>
+    <button type="button" class="clear-search">Clear search</button>
+  </div>
 {{else if eq .Tab "fav"}}
   <div class="empty"><strong>No favourites yet.</strong><p>Star a series to pin it here.</p></div>
 {{else if eq .Tab "new"}}